A depth gauge is a dedicated precision measuring instrument with a wide flat reference base and a sliding measuring rod that drops down into the feature being measured — a hole, a blind tapped hole, a counterbore, a milled slot, a step, a recess, an O-ring groove. The base bridges across the workpiece surface, the rod descends perpendicular to that reference, and the gauge reports how deep the rod has dropped below the base contact plane. It does what a caliper depth rod does, but with measurably better repeatability — and for routine depth measurement in a serious workshop, the dedicated depth gauge is the right tool.
This guide is the depth-measurement deep-dive for Australian fitters, toolmakers, machinists, fabricators and inspection departments. It explains how each type of depth gauge works (vernier, dial, digital workshop-tier and the Mitutoyo ABSOLUTE Digimatic premium tier), why a dedicated depth gauge beats a caliper depth rod for serious work (Practical Machinist consensus quoted in full with the geometry that drives it), how to use one without introducing the measurement errors that plague casual users, the JIS B 7518:2018 maximum permissible error specifications that govern depth gauge accuracy globally, the patent-protected Mitutoyo ABSOLUTE electromagnetic induction encoder technology that defines the practitioner gold standard, the difference between the Mitutoyo Series 547 (compact, fine resolution) and Series 571 (long-range, IP67 coolant-proof) that buyers regularly confuse, the counterbore and blind hole measurement challenges that no other guide covers honestly, the counterfeit Mitutoyo problem that floods online marketplaces, and how to choose between workshop-tier Dasqua and Maxigear stocked at AIMS and the premium Mitutoyo range available through our authorised supply chain.
Note on scope. This guide covers workshop depth gauges for precision engineering, machining, fabrication and inspection. It does not cover automotive tyre tread depth gauges — those are a separate consumer product class with accuracy specifications nowhere near workshop requirement, available from automotive retail rather than industrial supply. For caliper depth-rod fundamentals see our Vernier Caliper Guide, Dial Caliper Guide and Digital Caliper Guide. For height measurement work on a surface plate, see our Height Gauge Guide. For tighter-tolerance depth measurement than a depth gauge can deliver, see the depth micrometer section below.
The four depth gauge types — vernier, dial, digital, Mitutoyo ABSOLUTE — Quick Reference
Depth gauges divide into the same four readout families as calipers and height gauges. The mechanical structure — base, rod, fine-feed, locking screw — is essentially the same across all four.
| Type | How it reads | Typical accuracy | Best for | Trade-off |
|---|---|---|---|---|
| Vernier depth gauge | Main scale engraved on the rod; vernier scale on the base — read mechanically | JIS B 7518 — ±0.02 mm at ≤50 mm range (scale interval 0.02 mm) | Toolroom and inspection use, training apprentices on scale reading, environments hostile to electronics, no-battery field work | Slower to read than dial or digital. Requires practice. Parallax-prone. Older units may not zero on the workpiece reference — relative-zero workaround needed |
| Dial depth gauge | Rack-and-pinion drives a rotating dial face that gives the fractional reading below the main scale graduation | Similar to vernier — typically ±0.02 mm at ≤50 mm | Quick analog reading, comparative measurement against gauge blocks, no battery dependency, intuitive zero against a master | Rack-and-pinion mechanism is delicate. Chips and debris in the rack cause dial skip. Less common in modern AU industrial settings — most workshops have moved to digital for new purchases |
| Digital depth gauge (workshop tier) | Capacitive linear encoder drives an LCD display in mm or inches at the press of a button | Workshop-tier typical ±0.02 mm at ≤200 mm range | Fast measurement, mm/inch toggle, ABS/INC modes for comparative work, low skill floor — operators who are not trained on scale reading can read the display directly | Battery-dependent. Cheaper units can lose zero on power-off. Encoder may drift with heavy use over years. Workshop-tier accuracy is good but not at premium-tier level |
| Mitutoyo ABSOLUTE Digimatic | Mitutoyo's patented ABSOLUTE electromagnetic induction encoder — the same core technology across the Mitutoyo precision measuring line | Mitutoyo Series 547 ±0.02 mm at 0–200 mm; Series 571 ±0.03 mm at 0–300 mm typical | Inspection-grade work, production measurement, SPC data output, any application where the encoder must hold zero through power cycles and battery changes, and any environment where coolant or chip contamination is a concern (IP67 variants) | Premium pricing reflects the encoder technology, the IP67 environmental sealing, the manufacturing standard for base flatness and rod straightness, and the warranty/calibration certificate. Justified when accuracy and longevity matter |
What is a depth gauge — and what it is not
A depth gauge is a precision measuring instrument built around three functional elements. First, a wide, flat reference base (also called the beam or cross-bar) machined to a tight flatness specification and ground smooth on the bottom face. The base sits across the workpiece surface from which the depth is being measured. Second, a sliding measuring rod that descends from the base, perpendicular to the base plane, into the feature being measured. The rod tip is the contact point with the bottom of the feature. Third, a readout mechanism — vernier scale, dial face driven by rack-and-pinion, or digital encoder driving an LCD — that reports the depth the rod has dropped below the base reference plane.
Three workshop measurement applications dominate depth gauge use:
- Hole, counterbore and blind tapped hole depth — measuring how deep a feature extends below the workpiece surface. The base sits across the hole opening on the surrounding flat, the rod descends into the hole until it contacts the bottom, and the gauge displays the depth. Critical for counterbore depth (fastener seating), blind tapped hole drill depth (thread engagement), and pocket depth on CNC parts.
- Slot, recess and step measurement — measuring the depth of a milled slot, the height of a step on a turned shaft, or the depth of a recessed sealing surface. The base bridges across the feature on the higher reference surface.
- O-ring groove and sealing surface measurement — measuring the depth of grooves machined to accept O-rings or static seals. O-ring grooves have tight depth tolerance because the depth determines the compression on the seal — a 0.05 mm depth error on a critical O-ring groove can cause leakage or premature seal failure.
What a depth gauge is not — and this matters for buyers searching online — is a tyre tread depth gauge. The automotive consumer market sells small pocket depth gauges marked in 32nds of an inch or in millimetres for measuring tyre tread wear. These are not precision workshop instruments. They are consumer-tier tools with accuracy specifications in the range of plus or minus half a millimetre, designed for a measurement where the legal limit is 1.5 mm and the operator just needs to know whether the tyre is over or under the limit. For workshop depth measurement, tyre tread depth gauges deliver nowhere near the accuracy required. If you are checking tyre tread depth on a vehicle, the right tool is a tyre tread depth gauge from automotive retail. If you are checking machined feature depth on a workpiece, the right tool is a precision workshop depth gauge — which is what this guide covers.
A depth gauge is also not a caliper. Calipers have a depth rod that extends from the back of the slider, and a caliper can be used as a depth measuring tool in a pinch. But practitioners on Practical Machinist describe the caliper-depth-rod result as "ok but not great" compared with a dedicated depth gauge — and the next section explains why in detail. The geometry argument is decisive enough that toolrooms and inspection departments specify dedicated depth gauges rather than relying on calipers for depth work.
Depth gauge vs caliper depth rod — when the dedicated tool wins
Practical Machinist threads catalogue the same practitioner consensus on this question across hundreds of discussions: the dial caliper depth measurement, and inside measurements generally, are notoriously off without considerable practice and discipline. A caliper used for depth measurement is a compromise. The depth rod works, but it requires the operator to hold the caliper perfectly square to the reference surface — and the narrow caliper body does not enforce square automatically. Any tilt, any rocking, any movement during measurement introduces error. The cumulative result across many measurements is unreliable depth work.
A dedicated depth gauge solves the problem with geometry, not operator skill. The wide reference base spans the workpiece surface on both sides of the feature being measured. The base cannot tilt or rock — it sits flat across a span much wider than the feature. The measuring rod descends from the base perpendicular to the reference surface by mechanical constraint. The result is repeatable depth measurement that does not depend on the operator's ability to hold the gauge square.
The tilt error worked example
This is not a small effect. A 1-degree tilt error on a 25 mm depth measurement taken with a caliper depth rod introduces an error of about 0.0038 mm — small but visible on a 0.01 mm-resolution caliper. A 3-degree tilt on the same measurement introduces 0.034 mm error — well past the caliper's specified accuracy of plus or minus 0.02 mm under JIS B 7507:2022 for a 0–150 mm caliper. On a dedicated depth gauge with a 50 mm-wide base bridging across a 10 mm slot, achieving 3 degrees of tilt would require lifting one side of the base off the workpiece by more than 2.6 mm. Operators can see and feel that level of tilt and correct it before reading. The narrow caliper has no such mechanical feedback — the operator only knows the gauge is tilted by looking at the side.
The half-base hang-over rule from forum mining
Practical Machinist threads document a specific error mode worth flagging: measuring with half the depth gauge base hanging off the edge of the workpiece introduces approximately 0.0005 inch (0.013 mm) error compared to measuring with the base fully supported. This sounds counter-intuitive — the base is still flat against the reference surface — but the geometry shifts subtly when the unsupported side of the base flexes under the rod's spring pressure. For inspection-grade depth measurement, set the gauge up with the base fully across the workpiece reference plane, not balanced on the edge.
The measurement pressure differential
Depth measurement instruments apply different contact pressure depending on type. A depth micrometer (the precision tool above a depth gauge) applies 5 to 10 newtons of force through its ratchet stop. A depth gauge with a dial indicator readout applies 1 to 2 newtons through its internal spring. This 5-to-10× difference in measurement pressure is the reason depth indicators feel more consistent for routine work — the lighter spring force gives more reproducible "feel for the bottom" than the heavier micrometer ratchet. Practitioners on Practical Machinist describe reproducibility — getting the same answer twice in a row — as the hardest part of depth measurement, and lighter spring pressure consistently helps.
When the caliper depth rod is the right tool
- Occasional depth measurements — when you have a caliper in your hand and don't want to swap tools
- Quick approximate checks — confirming a feature is roughly to depth, not verifying inspection-grade accuracy
- Field service — when the toolbox only has space for one instrument
- Very narrow features the depth gauge base cannot span — the caliper depth rod fits holes down to about 4 mm where most depth gauge rods will not enter
- Edge features where there is no flat reference surface on both sides for the depth gauge base to bridge
When the dedicated depth gauge is the right tool
- Routine depth measurement — fitter or toolmaker checking many features per day
- Inspection-grade work — where depth measurement must be repeatable and meet a specified tolerance
- Critical depth dimensions — counterbore depth for fastener seating, blind tapped hole depth, O-ring groove depth, recess depth for sealing surfaces
- CNC setup and first-article verification — checking actual machined depths against drawing specification
- Comparative measurement — checking many parts against a master, with the gauge zeroed against a reference
Practitioners who do both kinds of work typically own both instruments. The caliper handles bench work where depth is a side-effect of the measurement. The depth gauge comes out when depth measurement is the actual point of the measurement.
The four depth gauge types — vernier, dial, digital, Mitutoyo ABSOLUTE
Depth gauges divide into the same four readout families as calipers and height gauges. The mechanical structure — base, rod, fine-feed, locking screw — is essentially the same across all four. Only the readout mechanism changes, and with it the operating characteristics, the accuracy specification, the price tier and the environmental tolerance.
| Type | How it reads | Typical accuracy | Best for | Trade-off |
|---|---|---|---|---|
| Vernier depth gauge | Main scale engraved on the rod; vernier scale on the base — read mechanically | JIS B 7518 — ±0.02 mm at ≤50 mm range (scale interval 0.02 mm) | Toolroom and inspection use, training apprentices on scale reading, environments hostile to electronics, no-battery field work | Slower to read than dial or digital. Requires practice. Parallax-prone. Older units may not zero on the workpiece reference — relative-zero workaround needed |
| Dial depth gauge | Rack-and-pinion drives a rotating dial face that gives the fractional reading below the main scale graduation | Similar to vernier — typically ±0.02 mm at ≤50 mm | Quick analog reading, comparative measurement against gauge blocks, no battery dependency, intuitive zero against a master | Rack-and-pinion mechanism is delicate. Chips and debris in the rack cause dial skip. Less common in modern AU industrial settings — most workshops have moved to digital for new purchases |
| Digital depth gauge (workshop tier) | Capacitive linear encoder drives an LCD display in mm or inches at the press of a button | Workshop-tier typical ±0.02 mm at ≤200 mm range | Fast measurement, mm/inch toggle, ABS/INC modes for comparative work, low skill floor — operators who are not trained on scale reading can read the display directly | Battery-dependent. Cheaper units can lose zero on power-off. Encoder may drift with heavy use over years. Workshop-tier accuracy is good but not at premium-tier level |
| Mitutoyo ABSOLUTE Digimatic | Mitutoyo's patented ABSOLUTE electromagnetic induction encoder — the same core technology across the Mitutoyo precision measuring line | Mitutoyo Series 547 ±0.02 mm at 0–200 mm; Series 571 ±0.03 mm at 0–300 mm typical | Inspection-grade work, production measurement, SPC data output, any application where the encoder must hold zero through power cycles and battery changes, and any environment where coolant or chip contamination is a concern (IP67 variants) | Premium pricing reflects the encoder technology, the IP67 environmental sealing, the manufacturing standard for base flatness and rod straightness, and the warranty/calibration certificate. Justified when accuracy and longevity matter |
For modern Australian workshops the practical choice is between workshop-tier digital (Dasqua and Maxigear at AIMS) and Mitutoyo Series 547 or 571 via the AIMS authorised supply chain. The vernier remains the right specification for two specific situations: training apprentices to read scales properly, and remote field environments where batteries cannot be replaced reliably. The dial depth gauge has largely been displaced by digital in new purchases but continues in service across many existing toolrooms. The detailed Mitutoyo Series 547 vs 571 differentiation — which model for which application — is covered in its own section below because buyers regularly confuse the two.
Depth gauge anatomy — the parts that determine accuracy
| Part | Function | What to watch for |
|---|---|---|
| Reference base (beam, cross-bar) | Wide flat reference surface that sits across the workpiece. Defines measurement zero — the base contact surface is the reference plane against which all depth measurements are referenced | Bottom face must be flat and clean. Mitutoyo Series 547 specifies base flatness within 5 µm. Burrs, wear or dirt on the base introduce systematic error. Wipe before every measurement. Hand-warming the base (especially on longer gauges) bends the base unevenly — handle by the base only on critical work |
| Measuring rod (depth blade) | Slides perpendicular to the base, dropping into the feature being measured. The rod tip is what contacts the bottom of the feature | Rod must be straight, slide freely, no lateral wobble. A bent rod cannot give accurate measurement and cannot be re-straightened to specification. Inspect after any drop. Practitioners also flag that the rod can spin at the depth contact point — note the rod's rotational position to avoid inconsistent contact |
| Main scale | Engraved on the rod, reading from the base contact surface. Whole millimetres on metric instruments, inches with subdivisions on imperial | Scale corrosion or paint wear on cheap instruments compromises reading. Quality gauges use hardened, satin-chromed rods that resist wear |
| Readout — vernier scale, dial face, or LCD | Reports the fractional measurement below the main scale graduation | Reading method varies by type. Vernier requires practice. Dial is easier. Digital is easiest. Mitutoyo Digimatic adds data output and ABS/INC modes |
| Fine-feed adjustment | Lets the operator advance the rod into the feature in small increments for precise final positioning without applying heavy pressure to the rod itself | Should move smoothly with no grit. Backlash should be minimal — visible play indicates wear. Practical Machinist threads identify gritty fine-feed feel as one of the early indicators of a counterfeit Mitutoyo |
| Locking screw | Clamps the rod in position so the gauge can be lifted clear of the feature for reading without losing the measurement | Light pressure only. Over-tightening damages the screw thread and can distort the rod. Always release before storing |
| Reference plane on the base bottom | The actual contact face that defines measurement zero. On Mitutoyo Series 547 this face is hardened, ground and lapped to manufacturing flatness specification | Wear or scratches on this face introduce systematic offset. A worn base reads consistently shallow or consistently deep depending on the wear pattern. Calibrate against gauge blocks after any visible damage |
| Interchangeable rod system (on some models) | Some depth gauges — including the Mitutoyo Series 218/129 and some Starrett models — use interchangeable measuring rods of different lengths to cover different depth ranges | Replaceable-rod gauges must be calibrated each time assembled. Set against gauge blocks to the major ranges of each rod (Practical Machinist consensus). Skipping this calibration is a common source of unexplained measurement error |
| Hook attachment (Mitutoyo Series 571 hook style) | Optional hook end on the rod for measuring step heights from above or for hard-to-reach features | Hook adds offset that must be calibrated — the gauge reads zero with hook flat against the reference, not with the rod fully retracted |
How to use a depth gauge — measurement procedure
The procedure is straightforward but the discipline matters. Practitioners on Practical Machinist and Hobby-Machinist emphasise the same handful of points repeatedly across hundreds of threads. The difference between a depth gauge that delivers its specified accuracy and a depth gauge that produces unreliable readings is almost always operator technique, not instrument fault.
Standard hole or counterbore depth measurement
Step 1 — clean. Wipe the workpiece reference surface where the base will sit. Wipe the bottom face of the base. Both must be free of chips, dust, oil residue and burrs. Dust particles in the workshop are routinely bigger than the acceptable measurement error on a quality depth gauge — they have to be removed before measurement.
Step 2 — remove burrs from the workpiece feature. A burr around the lip of the feature being measured prevents the depth gauge base from sitting flat across the surrounding reference plane. The gauge perches on the burr instead of on the reference plane, and the measurement is offset upward by the burr height.
Step 3 — release the rod. Loosen the locking screw so the measuring rod slides freely. Lift the rod clear of the base.
Step 4 — place the base. Position the depth gauge with the base sitting flat across the workpiece surface, centred over the feature being measured. The feature must fit within the slot in the base or be reachable by the rod through the gap. The base must span the feature on both sides — measuring with half the base hanging off the edge of the workpiece introduces approximately 0.0005 inch (0.013 mm) error per the Practical Machinist measurement.
Step 5 — lower the rod. Push the rod down gently until it touches the bottom of the feature. Use the fine-feed for the final approach — heavy finger pressure on the rod itself flexes the rod and gives shallow readings.
Step 6 — confirm contact. The rod should be in firm but not heavy contact with the feature bottom. You can feel the contact through the fine-feed knob. Excessive pressure deforms the rod tip or the feature surface. Insufficient pressure gives an inaccurate reading. Some rod tips will rotate at the contact point — note the rotational position and try to be consistent.
Step 7 — lock the rod. Tighten the locking screw gently to hold the rod in position.
Step 8 — read the gauge. Lift the gauge clear of the workpiece (the rod stays in position because of the lock screw). Read the depth on the scale, dial or display.
Step 9 — release the rod. Loosen the locking screw before returning the gauge to its case.
The two-handed discipline
One-handed operation is unreliable. Hold the base firmly with one hand on the workpiece — applying gentle downward pressure to keep the base flat against the reference — and manipulate the rod with the other hand. This is the Higher Precision practitioner reference point: proper depth measurements rely on the base sitting square to the reference surface, and one-handed operation cannot maintain that alignment reliably across the measurement. Two-handed technique is not optional for accurate work.
Confirm the reading
On a vernier gauge, confirm the vernier alignment under good light. On a dial gauge, confirm the dial pointer position cleanly without parallax. On a digital gauge, take two or three readings and confirm they agree within the gauge's resolution. A reading that doesn't repeat is a reading that hasn't been taken correctly — repeat the measurement until it does repeat, or investigate why it doesn't (most often: a burr, a tilted base, a rotating rod tip, or inconsistent measuring pressure).
Counterbore and blind hole depth measurement
The two most common depth gauge applications in Australian workshops are counterbore depth (for fastener seating) and blind hole depth (for thread engagement on tapped holes). Both come with specific challenges that go beyond general depth measurement technique.
Counterbore depth — fastener seating tolerance
A counterbore is the cylindrical recess machined to accept the head of a fastener (socket head cap screw, button head, or shoulder bolt). The counterbore must be deep enough that the fastener head sits flush with or slightly below the workpiece surface when fully tightened. Too shallow and the head protrudes above the surface — preventing mating parts from sitting flush, fouling movement, or simply looking unprofessional. Too deep and the fastener loses bearing area against the counterbore bottom, reducing joint strength.
The tolerance on counterbore depth is typically tight — often ±0.1 mm or tighter on a precision joint. A workshop-tier digital depth gauge at ±0.02 mm is comfortably within that envelope. A casual caliper-depth-rod measurement is not, particularly if the operator does not have the technique to hold the caliper square.
Blind hole depth — thread engagement
A blind tapped hole has the thread cut into a hole that does not pass through the workpiece. The drilled depth (before tapping) must be deeper than the required thread depth, because the tap has a chamfered lead-in that does not produce full thread. The thread depth itself must deliver the required thread engagement for joint strength — typically 1.5× to 2× the thread diameter for steel-in-steel, or up to 3× for steel-in-aluminium.
The depth gauge confirms the drilled hole depth after drilling and before tapping (so the tap has clearance to reach full depth) and confirms the actual usable thread depth after tapping (so the joint will deliver its design strength). Both measurements need to be reliable — a 1 mm error on a blind tapped hole drilled for 10 mm of thread engagement compromises the joint by 10%, which is meaningful on safety-critical fastener joints.
The trapped air and fluid trap problem
Quality Magazine and depth measurement specialists flag a specific challenge on close-tolerance blind holes: cutting fluids or air can become trapped at the bottom of the hole, preventing the depth gauge rod from reaching the actual feature bottom. The result is a false-shallow reading — the gauge reports the depth at which the trapped fluid or air stopped the rod, not the actual hole depth.
The defence is to clean the hole thoroughly before measurement. Blow compressed air into the hole to clear cutting fluid and chips. Tip the workpiece if the hole orientation allows trapped air to escape. On precision inspection work, measure twice with the part oriented differently between measurements to confirm the readings agree — if they disagree, trapped fluid or air is the likely cause.
The radius problem
If the rod tip lands on a radius (corner) at the bottom of the feature rather than on the true flat bottom, the gauge reads shallow. This happens on counterbores where the cutter has left a fillet at the corner between the bore and the bottom face, and on blind holes where the drill point geometry leaves a conical bottom rather than a flat bottom.
On blind holes drilled to depth, the depth gauge should be moved laterally within the hole if possible to confirm the rod is reaching the lowest point of the conical drill-point geometry. On counterbores, the gauge rod tip should sit on the flat bottom of the bore, away from the corner radius. Practitioners on Practical Machinist describe the rod-on-radius scenario as a false "not deep enough" reading — the gauge thinks the feature is shallower than it actually is because the rod is supported on the radius rather than the flat.
Depth gauge accuracy — JIS B 7518:2018 and ISO 13225
Depth gauge accuracy is governed internationally by JIS B 7518 (the Japanese Industrial Standard for vernier, dial and digital depth gauges, current edition JIS B 7518:2018 with JIS B 7518:2023 released as the newer edition) and ISO 13225:2012 (the international standard for dimensional measuring equipment including caliper depth gauges and height gauges). Despite being a Japanese standard, JIS B 7518 is the de facto global reference for depth gauge specifications because of Mitutoyo's market dominance and because of Mitutoyo's role in developing the standard. There is no Australian Standard specific to depth gauges. AU industry uses JIS B 7518 and ISO 13225 as the reference, with Mitutoyo's published specifications functioning as the practical benchmark across the AU workshop sector.
JIS B 7518:2018 maximum permissible error — actual table
The standard sets maximum permissible error (MPE) of the indication value, based on measurement depth and scale interval. The values below are taken directly from JIS B 7518:2018 Table 1 (millimetres):
| Measurement depth | MPE — scale interval 0.05 mm | MPE — scale interval 0.02 mm or 0.015 mm |
|---|---|---|
| 50 mm or less | ±0.05 | ±0.02 |
| Over 50 to 100 mm | ±0.06 | ±0.03 |
| Over 100 to 200 mm | ±0.07 | ±0.03 |
| Over 200 to 300 mm | ±0.08 | ±0.04 |
| Over 300 to 400 mm | ±0.09 | ±0.04 |
| Over 400 to 500 mm | ±0.10 | ±0.05 |
| Over 500 to 600 mm | ±0.11 | — |
The standard distinguishes by scale interval (resolution) rather than just by measurement range. A vernier depth gauge with 0.02 mm scale interval has tighter MPE than a vernier gauge with 0.05 mm scale interval — but only over the shorter measurement ranges where the finer resolution is meaningful. Digital depth gauges with 0.01 mm resolution display values smaller than 0.02 mm, but the JIS B 7518 MPE specification applies to the gauge's indication accuracy, not just to its display resolution.
What this means in practice
A workshop-tier Dasqua Vernier Depth Gauge 300 mm with 0.02 mm graduation, used at 100 mm measurement depth, is specified to plus or minus 0.03 mm under JIS B 7518:2018. A Mitutoyo Series 547 ABSOLUTE Digimatic with 0.01 mm resolution at the same 100 mm depth is specified to plus or minus 0.02 mm — the better encoder gets you a tighter MPE within the standard's framework.
For tolerances tighter than the depth gauge specification can deliver, the step up is a depth micrometer. ISO 3611 specifies depth micrometers to approximately plus or minus 0.005 mm over a 25 mm rod range — roughly an order of magnitude tighter than a depth gauge. Depth micrometers use interchangeable measuring rods to cover different depth ranges and are the workshop standard for precision-tolerance depth measurement. AIMS stocks the Dasqua Depth Micrometer (Metric) and Dasqua Depth Micrometer (Imperial) for these applications.
The hand-warming effect on accuracy
All MPE specifications assume the gauge is at the reference temperature of 20 degrees Celsius. The reality of workshop use is that the gauge is rarely at exactly that temperature — and on longer gauges, the operator's hands warming the base introduces measurable error. A 300 mm depth gauge column warmed by 5 degrees Celsius through hand contact will expand by approximately 0.018 mm. On a measurement specified to plus or minus 0.04 mm at that range, the thermal effect consumes nearly half the available tolerance budget.
For inspection-grade work the discipline is to handle the gauge by the base only, allow it to stabilise at workshop temperature before measurement, and wear gloves where prolonged handling is unavoidable. For routine workshop measurement the effect is small and usually not noticed — but practitioners flag it for the inspection bench because the cumulative effect across many measurements is enough to fail a part that should have passed.
Mitutoyo Series 547 vs Series 571 — the differentiation buyers confuse
Mitutoyo's premium digital depth gauge line splits into two product series — 547 and 571 — that solve different problems. Buyers regularly assume they are variants of the same gauge. They are not. Specifying the wrong series for the application is the most common Mitutoyo depth gauge purchase error.
Mitutoyo Series 547 — compact ABSOLUTE Digimatic
The 547 series is Mitutoyo's compact, fine-resolution ABSOLUTE Digimatic depth gauge. Designed for general workshop and toolroom depth measurement where accuracy and reading speed both matter but the work is typically within standard depth ranges.
- Resolution: 0.001 mm, 0.01 mm, 0.00005 inch or 0.0005 inch depending on model variant. The finest resolution options live in this series.
- Range: 0–200 mm typical, with extension rod sets to extend reach.
- Base flatness: 5 µm (manufacturing specification).
- Measuring force: 1.4 to 1.5 newtons — lighter than depth micrometers, contributes to repeatable feel for the bottom.
- Battery life: approximately 3.5 years under normal use. ABSOLUTE encoder draws minimal current.
- Encoder: Mitutoyo capacitive Digimatic with ABSOLUTE position memory.
- Best for: toolroom, inspection bench, general workshop where compact size and fine resolution matter more than long range or aggressive environmental protection.
Mitutoyo Series 571 — long-range ABSOLUTE Digimatic with IP67
The 571 series is Mitutoyo's long-range, environmentally hardened ABSOLUTE Digimatic depth gauge. Designed for production inspection and CNC workshop use where measurements may be needed at long ranges, coolant exposure is routine, and the encoder must hold zero through power cycles and battery changes.
- Resolution: 0.01 mm (single resolution option — the series is not designed for sub-micron resolution work).
- Range: 0–150 mm, 0–200 mm, 0–300 mm, 0–600 mm and 0–1000 mm versions. Long-range coverage is the defining feature of the series.
- Battery life: approximately 20,000 hours (about 3 years).
- Encoder: Mitutoyo ABSOLUTE electromagnetic induction encoder (the patent-protected technology — see next section).
- IP rating: IP67 coolant-proof variants available — the encoder is unaffected by coolant or chip contamination during use.
- Hook-style models: available for measuring step heights from above or for hard-to-reach features.
- Best for: CNC inspection bench in coolant-exposed environments, large fabrication where long-range depth measurement is routine, production inspection where the encoder must hold zero through shift changes and battery swaps.
Which to specify — the buying decision
| Application | Recommended series | Why |
|---|---|---|
| Toolroom depth measurement at 0–200 mm, dry environment, fine resolution required | Series 547 | Compact size, 0.001 mm resolution available, lighter measuring force, sufficient range |
| CNC inspection bench with coolant exposure, 0–200 mm | Series 571 IP67 | Coolant proofing essential. 0.01 mm resolution is enough for typical CNC inspection tolerances |
| Large fabrication depth measurement at 0–600 mm or 0–1000 mm | Series 571 | Series 547 does not cover these ranges. 571 is the only Mitutoyo digital option above 200 mm |
| Production inspection — multi-shift, many operators, battery-life is a service consideration | Series 571 | Electromagnetic induction encoder has longer battery life under heavy use than capacitive Digimatic, and is unaffected by contamination |
| Inspection-grade calibration lab — sub-micron resolution required | Series 547 with 0.001 mm model | Finest resolution option in the Mitutoyo depth gauge line, suitable for inspection-grade calibration work |
| Step height measurement from above the workpiece | Series 571 hook-style | Hook attachment is the 571-specific feature for this application |
Mitutoyo ABSOLUTE encoder technology — patent-protected differentiator
The Mitutoyo ABSOLUTE encoder is the technical differentiator that justifies the premium price across the Mitutoyo precision measuring line — calipers, micrometers, indicators, height gauges, depth gauges and linear scales. Understanding what makes it different from standard capacitive encoders explains why practitioners on Practical Machinist consistently recommend Mitutoyo for inspection-grade work.
The patent
The technology is covered by US Patent 8,847,583 B2 and US Patent 8,928,311 B2 (assigned to Mitutoyo Corporation, August 2012). The patents describe an electromagnetic induction type absolute position measuring encoder using scale coils, transmitter and receiver coils, and flux change detection mechanisms. The encoder is described in the patent as "suitable for use in electronic digital calipers, indicators, linear scales, micrometers" — and depth gauges sit in the same product family.
How it works — and why it matters
Standard capacitive encoders read position by measuring capacitance changes between conductive patterns on the moving scale and stationary electrodes. The technology works well in clean conditions, but coolant, cutting fluid, swarf or even dust can disrupt the capacitive coupling and corrupt the position reading. Standard encoders also require the instrument to be powered on and driven to a known reference position before each measurement session — battery removal or power loss means the encoder loses its position and must be re-zeroed.
The Mitutoyo ABSOLUTE electromagnetic induction encoder operates on a different physical principle. The scale carries a precise pattern of conductive coils; the read head contains transmitter and receiver coils. The electromagnetic induction coupling between these coils encodes absolute position — the instrument knows exactly where it is the moment power is applied, with no reference drive required. The patent documentation describes the encoder as "unaffected by contamination, unlike previous encoders, allowing for smooth, stable operation without needing to reset the origin."
Practical implications for depth measurement
- Position known on power-up — turn on the depth gauge, place it on the workpiece, take the measurement. No driving to a reference point first. No re-zeroing after a battery change.
- Coolant-proof operation — in IP67 variants on the Series 571, the encoder operates reliably while the instrument is exposed to coolant. The encoder doesn't drift, lose position or corrupt readings even when actively contaminated.
- Long battery life — the electromagnetic induction encoder draws minimal current, contributing to the 3+ year battery life specifications across the Mitutoyo ABSOLUTE line.
- Lifetime origin retention — the encoder keeps track of the origin point once set, for the entire life of the battery. A measurement zero established at calibration time is still the zero five years later, even after dozens of battery changes.
This is the technical foundation underneath the practitioner consensus that Mitutoyo is the inspection-grade depth gauge worth investing in. Workshop-tier digital depth gauges using standard capacitive encoders are good tools — but they cannot match the ABSOLUTE encoder's behaviour under contamination, power cycling and long-term position retention. For depth measurement in a CNC inspection environment where coolant exposure is routine, the difference is operational.
Mitutoyo depth gauge product line — Series 527, 547, 571, 7211, 218 and 7210
Mitutoyo's depth gauge product line covers the full application spectrum from workshop training to inspection-grade CNC production. Six product series serve different needs:
Mitutoyo Series 527 — vernier depth gauges
The 527 series is Mitutoyo's vernier depth gauge family — the workhorse vernier specification when a mechanical-scale instrument is the right choice. Available in 0–150 mm, 0–200 mm, 0–300 mm, 0–600 mm and 0–1000 mm column heights. Hardened, satin-chromed rods. Available with metric, imperial, or dual metric/imperial scales. The 527 series is the global teaching reference for vernier depth measurement and remains in service across many AU toolrooms.
Mitutoyo Series 547 — compact ABSOLUTE Digimatic depth gauge
Covered in detail in the section above. Compact, fine-resolution (0.001 mm available), 5 µm base flatness, 1.4 N measuring force, 3.5 year battery life, 0–200 mm typical range. The workshop and toolroom premium digital specification when range is moderate and resolution matters.
Mitutoyo Series 571 — long-range IP67 ABSOLUTE Digimatic depth gauge
Covered in detail above. Long-range (up to 0–1000 mm), IP67 coolant-proof, electromagnetic induction ABSOLUTE encoder, hook-style variants available. The CNC inspection and production specification.
Mitutoyo Series 7211 — dial depth gauge
The 7211 series is Mitutoyo's dial depth gauge family — rack-and-pinion driven dial face below the main scale. Less common in new specifications than the 547 ABSOLUTE Digimatic but maintained in the Mitutoyo range for users who specifically want a dial display. The rack-and-pinion mechanism makes the 7211 series more vulnerable to chip and debris contamination than digital alternatives — care matters more on this series than on the 547 or 571.
Mitutoyo Series 218 / 129 — depth gauges with interchangeable measuring blades
The 218 and 129 series use interchangeable measuring blades or rods of different lengths. Useful in production environments where the same gauge is used to measure features of widely varying depth (a long rod for deep holes, a shorter rod for shallow features) and in applications where the rod is exposed to damage and replaceability matters. Lower-volume specification than the 527 and 547 series. Critical note from Practical Machinist: replaceable-rod gauges must be calibrated each time the rods are assembled or interchanged, set against gauge blocks to the major ranges of each rod. Skipping this calibration step is a common source of unexplained measurement error.
Mitutoyo Series 7210 — dial-type depth gauge
The 7210 series is a related dial depth gauge variant in the Mitutoyo line, with specific application focus on production environments where the dial readout is preferred over digital. Listed for completeness — the more common specifications are 547 digital and 527 vernier.
Mitutoyo vs Starrett vs Brown & Sharpe — the practitioner brand reality
Practical Machinist consistently identifies three brands as the premium-tier depth gauge specification: Mitutoyo, Starrett and Brown & Sharpe. Each has a distinct character and a distinct strength. The choice between them on a serious workshop or inspection bench is more about workflow preference than about any one brand being better in absolute terms.
| Brand | Practitioner positioning | Best for | Trade-off |
|---|---|---|---|
| Mitutoyo | Precision inspection benchmark. Higher resolution and repeatability. Advanced sensor technology (ABSOLUTE encoder). Calibration traceability and consistency across the global product line | Inspection labs, CNC production, quality bench, any application where the ABSOLUTE encoder and Mitutoyo's manufacturing standard are operational requirements | Premium pricing. Less of the "feels like a workshop tool" weight and finish that Starrett delivers. Newer-generation electronics may seem less "purpose-built" than the classic Starrett designs |
| Starrett | Mechanical consistency rather than ultra-high digital precision. The classic workshop bench feel — solid weight, hardened finish, "feels purpose-built in a tradesperson's hand." Starrett 449 vernier is a US benchmark vernier depth gauge at 0–3 inch or 0–6 inch with 0.001 inch resolution and ±0.0001 inch accuracy | Workshop bench, toolroom, fitter who values mechanical solidity over digital features, training environment where the instrument's classic feel matters | Heavier than Mitutoyo. Less data output capability on digital variants. Premium pricing similar to Mitutoyo but the value proposition is different |
| Brown & Sharpe | Significantly more durable and accurate per practitioner consensus. Premium-premium tier — above Mitutoyo and Starrett in price. Hand-tool feel that practitioners describe as "noticeably better" than either Mitutoyo or Starrett | Critical inspection work where the additional durability and accuracy justify the price premium. Calibration laboratories. High-volume production inspection where instrument longevity is the dominant cost factor | Significantly more expensive than Mitutoyo. Smaller product range — fewer specialty configurations available. Lower brand presence in AU industrial supply than Mitutoyo |
Other brands in service across AU workshops include Moore & Wright (UK, traditional workshop tier with a long heritage), Fowler (US distributor with a mixed product line — some genuinely good gauges, some rebadged workshop tier), SPI / Swiss Precision Instruments (mid-tier with calibration certificates available), Tesa (Swiss premium, less common in AU), and Hommel (German, specialty). For most AU workshop buyers the practical choice is Mitutoyo through AIMS's authorised supply chain, with Starrett available as a specialty source-on-request for applications where the Starrett feel is specifically wanted.
⚠️ The counterfeit Mitutoyo problem — and how to spot a fake in 30 seconds
Counterfeit Mitutoyo precision measuring instruments — including depth gauges — flood eBay, Amazon Marketplace, AliExpress and grey-market sellers in numbers that dwarf the genuine market. Practical Machinist and Home Shop Machinist BBS threads catalogue the counterfeit problem across the entire Mitutoyo small-tools range. Mitutoyo Corporation maintains an official spot-the-fake page because the problem is that pervasive. Buying from an unauthorised source means a real risk of receiving an unbranded workshop-tier instrument with a forged Mitutoyo logo, a forged serial number, a generic plastic case, no calibration certificate, and no warranty backing — at a Mitutoyo-tier price.
The economics drive the counterfeit market. A genuine Mitutoyo Series 547 or 571 depth gauge from an authorised distributor is many times the price of a workshop-tier alternative. A counterfeit on eBay or Amazon is often priced at workshop-tier rates, sometimes cheaper. To the unwary buyer this looks like a bargain. In reality the buyer is getting an unbranded workshop-tier instrument with a Mitutoyo logo applied — not a Mitutoyo, and the measurements it produces should not be treated as Mitutoyo-grade.
The deliberate misspellings are the trade's hallmark. Amazon and eBay listings appear under "Mitutogo", "MITU-tyo", "Mituttoyo", "Mito_tuyo" and other variants designed to slip past Mitutoyo's trademark enforcement while still attracting keyword search traffic. If the spelling on the instrument or its packaging does not exactly match Mitutoyo, it is not a Mitutoyo. No exceptions. Mitutoyo does not produce sub-brands or variants under altered spellings.
The five-check spot-the-fake procedure
| Check | Genuine Mitutoyo | Counterfeit |
|---|---|---|
| 1. Rod fit and feel | Rod slides smoothly through the base with no lateral wobble. Mechanical fit is tight | Rod has visible lateral slop in the base. Movement feels gritty rather than smooth |
| 2. Fine-feed knob feel | Fine-feed rotates with a smooth, slightly heavy, glass-like feel. No grit, no skipping | Fine-feed has a gritty, hesitant feel. Sometimes catches and releases as it rotates |
| 3. "Made in Japan" stamp | Plastic case has "Made in Japan" clearly stamped or moulded on the underside. The instrument itself has Japan marking visible on the base | Case underside has no country-of-origin marking, or has a sticker (not moulded text) that peels off easily |
| 4. Base flatness and finish | Base bottom face has the Mitutoyo satin-chrome finish and is ground flat to a measurable specification (5 µm on the Series 547). The base sits without rocking on a flat reference surface | Base finish is duller. Bottom face may rock slightly on a flat reference — the base is not actually flat to specification |
| 5. Serial number quality | Serial number is crisply etched, centred, in the correct Mitutoyo font, and matches Mitutoyo's serial number format for the specific model series (547, 571, 527 etc.) | Serial number is often fuzzy, off-centre, in the wrong font, or appears to have been added after manufacturing rather than during it |
The documentation check
A genuine Mitutoyo depth gauge ships with a Mitutoyo-branded plastic case, a Mitutoyo calibration inspection certificate with traceable serial number that matches the instrument, a Mitutoyo instruction sheet in multiple languages, and Mitutoyo-branded accessories where applicable (extension rods, hook attachments). Counterfeits typically ship in a generic plastic case with no documentation, or with photocopied documentation that does not match Mitutoyo's printing standards. If the calibration certificate is missing or looks photocopied, the instrument is almost certainly not authentic.
The single safest defence is to buy only from authorised Australian distributors. Eliminate eBay, Amazon Marketplace, AliExpress and grey-market sellers from your consideration regardless of how attractive the price looks. AIMS sources Mitutoyo through our authorised supply chain — every Mitutoyo depth gauge supplied through AIMS comes with genuine documentation, calibration certificate, and full manufacturer warranty intact.
Authorised Mitutoyo supply in Australia
The single safest defence against counterfeit Mitutoyo depth gauges is to buy only from authorised Australian distributors. Mitutoyo maintains an authorised distributor network in Australia for its precision measuring small tools — calipers, micrometers, dial indicators, gauge blocks, height gauges, depth gauges and the rest of the small-tools range. Anything sold under the Mitutoyo name in Australia that is genuine and warranty-backed will have come through this authorised channel.
For capital-equipment Mitutoyo products (Coordinate Measuring Machines, Vision Measuring Systems, Hardness Testing Systems, Form Measuring Machines, Profile Projectors and similar), buyers can purchase either directly from Mitutoyo Asia Pacific or through an authorised distributor — either path leads to authorised, warranty-backed equipment.
AIMS sources Mitutoyo through our authorised supply chain
AIMS Industrial supplies Mitutoyo precision measuring tools through our authorised supply chain. The Mitutoyo depth gauges, calipers, micrometers, indicators and other small tools we supply are guaranteed-genuine, Japan-manufactured, Mitutoyo-warranty-backed instruments with the manufacturer calibration certificate included. No counterfeit risk, no grey-market exposure, no questions about provenance.
AIMS is in the process of bringing the Mitutoyo depth gauge range into our online store. Until the range is fully loaded with Shopify product pages, Mitutoyo depth gauges are available on request — contact the AIMS team on (02) 9773 0122 or via the contact page for current availability, model selection advice, lead times and quotation. We can supply any Mitutoyo Series 527 vernier, Series 547 ABSOLUTE Digimatic, Series 571 long-range or IP67 variant, Series 7211 dial, Series 7210 dial-type, or Series 218/129 interchangeable-rod depth gauge with the manufacturer warranty intact.
Angular and protractor depth gauges — combination workshop tools
A specialty subclass of depth gauge combines depth measurement with angle measurement, using a protractor head that can be set to a specific angle relative to the rod. The tool measures depth along an angled reference surface — useful in fabrication, sheet metal work, welding fit-up and toolmaking where angled features need their depth verified.
AIMS stocks three Maxigear combination depth gauge / protractor tools:
- Maxigear 90 x 50 x 150 mm Rectangular Head Depth Gauge Protractor — combination tool with rectangular reference head and 150 mm depth blade. Best for measurements where the rectangular head can sit flat across a square or rectangular reference surface.
- Maxigear 150 mm Round Head Depth Gauge Protractor — round head variant of the same combination tool, useful where the rectangular head will not fit the reference surface (around radii, in confined spaces).
- Maxigear Angular Depth Gauge — dedicated angular depth gauge for measuring depth on angled features without the protractor functionality. Simpler tool when the angle is fixed and known.
The combination tools are workshop-tier instruments — Maxigear quality, suitable for fabrication, sheet metal work and light toolroom use. For inspection-grade angular depth measurement, standard practice is to use a precision angle plate plus a separate dedicated depth gauge or depth micrometer rather than relying on a combination tool. Angular measurement and depth measurement combined on a single instrument compounds errors in both axes — the angle setting introduces uncertainty, and the depth measurement against the angled reference introduces further uncertainty. For routine workshop use the combination tool is fine; for inspection-grade work decouple the two measurements.
Depth gauge calibration — JIS-compliant procedure and AU traceability
Depth gauge calibration is the process of verifying that the gauge's indicated value agrees with the actual depth being measured, within the MPE specified by JIS B 7518. Calibration is not just a one-time factory operation — it is a recurring discipline that maintains the gauge's accuracy across its working life.
Calibration cadence by application
| Application | Calibration interval | Notes |
|---|---|---|
| High-use production line | Every 6 to 12 months | Heavy use accelerates wear on the base, rod and reference surfaces. Coolant exposure (non-IP-rated gauges) further reduces interval |
| Inspection-grade tool | Annually, minimum | Required by ISO 9001 quality systems and similar frameworks. Annual NATA-accredited calibration with certificate is the AU industry standard |
| Routine workshop use | Annually | Reasonable interval for general use. More frequent if used in harsh environments |
| Hobby or low-volume use | Every 2–5 years | Or whenever the gauge has been dropped, shows visible damage, or readings appear inconsistent |
| Replaceable-rod gauges (Mitutoyo 218, Starrett rod sets) | Each time rods are reassembled | Critical — Practical Machinist consensus. Each rod must be set against gauge blocks to the major ranges of that rod after assembly |
| Digital gauges in coolant or harsh environments | More frequent than the above intervals | Encoder drift, IP seal degradation, battery contact corrosion can all degrade performance faster in harsh conditions |
Calibration procedure
The standard calibration procedure measures the gauge's output against certified gauge blocks at multiple points across the gauge's measurement range. Typical points include zero (base flat against the surface plate), 10%, 25%, 50%, 75% and 100% of full range. The indicated value is recorded against the known gauge block value, and the difference is the error at that point. If all measured points are within MPE, the gauge passes calibration. If any point exceeds MPE, the gauge is adjusted (where adjustable) or flagged as out of tolerance.
For inspection-grade traceability the calibration is performed by a NATA-accredited calibration laboratory using gauge blocks with their own traceability to the Australian national measurement standard. The calibration certificate states the measurement uncertainty at each tested point and references the calibration laboratory's NATA accreditation number. This certificate is the auditable evidence that the gauge meets its specification — required for ISO 9001 quality system compliance and for any safety-critical measurement.
The replaceable-rod calibration trap
Practical Machinist threads repeatedly flag a specific calibration trap that catches users of replaceable-rod depth gauges and depth micrometers. The gauge as a system needs to be calibrated, not just the body. Each measuring rod, when assembled into the body, must be checked against gauge blocks set to the major ranges of that rod. A 0–25 mm rod in the same body as a 25–50 mm rod gives different measurements because of small differences in how each rod seats in the body. Skipping the per-rod calibration when reassembling is a common source of unexplained measurement error.
Care and maintenance — keeping a depth gauge accurate for decades
A quality depth gauge cared for properly will outlast its owner. The discipline is the same set of habits that apply to all precision measuring instruments, with a few depth-gauge-specific points worth highlighting.
- Always store in the case. The case keeps the gauge away from chips, grit, dust and impact. Never store loose in a toolbox drawer where other tools can bang against the rod or the base.
- Clean the base before every measurement. Wipe the bottom face of the base with a clean dry rag. The bottom face is the measurement reference; anything on it introduces error. Practitioner reality from forum mining: dust particles in the workshop are routinely bigger than the acceptable measurement error on a quality gauge.
- Clean the workpiece reference surface. Burrs, chips and dirt on the workpiece all introduce measurement error. Wipe before placing the gauge. Remove burrs around the feature being measured before the gauge is brought to it.
- Do not drop the gauge. Dropping bends the measuring rod or distorts the base. A bent rod cannot be straightened back to specification. After any drop — even a short one onto a soft surface — run a calibration check against gauge blocks before further use.
- Use the fine-feed for final positioning. Pushing the rod by hand to seat it against the feature bottom deforms the rod and gives shallow readings. The fine-feed is what gives consistent contact pressure.
- Do not over-tighten the lock screw. Light pressure to hold position is enough. Over-tightening damages the screw thread and can distort the rod.
- Release the rod before storing. Storing with the rod clamped puts continuous stress on the lock mechanism, accelerating wear on the screw and the rod surface contacted by the screw tip.
- Replace damaged rod tips. A burred or chipped rod tip lays the contact point off the rod centreline, introducing measurement error. Most quality depth gauges allow rod tip replacement — confirm the specific model's parts availability before sourcing.
- Avoid hand-warming on critical work. Handle the gauge by the base only on inspection-grade work. Allow the gauge to stabilise at workshop temperature before measurement. For long-range gauges (300 mm and above) the thermal effect on accuracy is enough to matter.
- Schedule periodic calibration. Use the table in the calibration section above to set the interval appropriate to your application.
Common depth gauge mistakes and how to avoid them
| Mistake | Why it matters | Fix |
|---|---|---|
| Using a caliper depth rod when a dedicated depth gauge is the right tool | Caliper depth measurements are notoriously off without considerable practice (Practical Machinist consensus). Tilt error can exceed caliper accuracy specification | Use a dedicated depth gauge for routine depth work. Reserve the caliper depth rod for occasional measurements where precision is not critical |
| Pushing the rod too hard onto the feature bottom | Heavy pressure flexes the rod and gives a shallow reading. The reading does not represent actual feature depth | Use the fine-feed for the final approach. The rod should touch the feature bottom firmly but not heavily — feel the contact through the fine-feed knob |
| Dirty base on the workpiece surface | Any film, burr or chip under the base is unknown packing — the measurement is offset by that thickness | Wipe both the base and the workpiece surface before measurement. Inspect both for burrs and chips |
| Burrs around the feature being measured | Burr around the lip of the feature prevents the base from sitting flat on the surrounding reference plane. The gauge perches on the burr, measurement is offset upward | Deburr the workpiece feature before measurement. Particularly important on parts straight off the machine where burrs from drilling, tapping or milling are still present |
| One-handed operation | Cannot maintain square reference under the gauge. Reading varies depending on how the gauge is held | Hold the base firmly with one hand on the workpiece, manipulate the rod with the other hand. Two-handed technique is the practitioner standard, not optional |
| Half-base hanging off the workpiece edge | Introduces approximately 0.0005 inch (0.013 mm) error compared to a fully supported base (Practical Machinist measurement) | Set up the gauge with the base fully across the workpiece reference plane. Not balanced on the edge with half the base unsupported |
| Rod tip on a radius rather than the flat bottom | False "not deep enough" reading. The rod is supported on the corner radius rather than reaching the actual feature bottom | Move the rod laterally within the feature to find the true lowest point. On counterbores with corner fillets, ensure the rod sits on the flat bottom away from the corner |
| Trapped fluid or air on close-tolerance blind holes | Cutting fluid or trapped air prevents the rod from reaching the feature bottom. Gauge reads false shallow | Blow out the hole with compressed air before measurement. Tip the workpiece if orientation allows trapped air to escape. Measure twice with the part oriented differently to confirm readings agree |
| Heating the gauge with hands | Thermal expansion adds error, particularly noticeable on long gauges (300 mm and above). 5°C warming of a 300 mm column adds ~0.018 mm | Handle the gauge by the base. Allow it to stabilise at workshop temperature before measurement. Wear gloves on critical inspection work |
| Reading the vernier scale under poor light | "Looks close" is not "lines up exactly". Reading errors of one division are common with vernier gauges | Read under good light. Use a magnifier where needed. Confirm vernier alignment carefully before recording |
| Skipping per-rod calibration on replaceable-rod gauges | Each rod-in-body combination has slightly different seating behaviour. Skipping calibration after rod change is a common source of unexplained error (Practical Machinist consensus) | Calibrate against gauge blocks each time rods are assembled or interchanged. Check at major ranges of each rod |
| Storing with the rod clamped in position | Continuous stress on the lock mechanism degrades it over time. Wear at the screw-tip contact point on the rod accelerates | Release the lock screw before returning the gauge to its case |
| Buying a counterfeit Mitutoyo at workshop-tier price | You get an unbranded workshop-tier instrument with a forged Mitutoyo logo, no warranty, no certificate, no provenance | Buy only from authorised AU distributors. Run the five-check spot-the-fake procedure on any Mitutoyo of uncertain origin. Confirm spelling exactly matches "Mitutoyo" |
| Treating workshop-tier accuracy as inspection-grade | A workshop-tier digital depth gauge is good to about ±0.02 mm at moderate ranges. Inspection-grade tolerance of ±0.005 mm needs a depth micrometer, not a depth gauge | Match the instrument to the tolerance. Use a depth micrometer for tight-tolerance work. Use a Mitutoyo 547 ABSOLUTE Digimatic for tight digital depth gauge work |
| Specifying Series 547 when the application actually needs Series 571 | 547 is compact, fine-resolution, 0–200 mm. 571 is long-range and IP67. Choosing 547 for a CNC coolant environment or for a 600 mm measurement range means buying the wrong tool | Read the Series 547 vs Series 571 section above before specifying. The differentiation is consequential |
| Using a tyre tread depth gauge for workshop measurement | Tyre depth gauges are automotive consumer-tier instruments with accuracy nowhere near workshop requirement | Use the right tool. Tyre depth gauges are for tyre tread; workshop depth gauges are for machined features |
AIMS depth gauge range — Dasqua, Maxigear and Mitutoyo via authorised supply
AIMS Industrial supplies depth gauges across three tiers: workshop-tier Dasqua and Maxigear (stocked online for immediate dispatch), specialty combination tools (Maxigear angular and protractor heads, stocked online), and premium-tier Mitutoyo (available through AIMS via our authorised supply chain, sourced on request through our sales team).
Workshop tier — dedicated depth gauges, stocked online
- Dasqua Vernier Depth Gauge 300 mm Range 0.02 mm Graduation — 0–300 mm vernier depth gauge with 0.02 mm scale interval. JIS B 7518 ±0.03 mm MPE at 100 mm depth. The workshop default for trade training, general fitting and routine layout work. Hardened steel construction, supplied in a fitted case.
- Maxigear Digital Depth Gauge — digital LCD readout with mm/imperial toggle, ABS/INC modes for comparative measurement, hardened steel base and rod. Workshop-tier digital accuracy for fast measurement. The right tool when reading speed matters and operators may not be trained on scale reading.
Specialty — angular and protractor combination tools, stocked online
- Maxigear 90 x 50 x 150 mm Rectangular Head Depth Gauge Protractor — combination depth gauge and protractor with rectangular reference head and 150 mm blade.
- Maxigear 150 mm Round Head Depth Gauge Protractor — round head variant of the combination tool.
- Maxigear Angular Depth Gauge — dedicated angular depth gauge without protractor functionality.
Adjacent precision — depth micrometers for tight-tolerance work
For depth measurements requiring tolerance tighter than a depth gauge can deliver (typically below 0.02 mm), the right tool is a depth micrometer. AIMS stocks two Dasqua depth micrometers online:
- Dasqua Depth Micrometer – Metric — interchangeable rod set covering 0–100 mm or 0–150 mm depending on configuration, 0.01 mm resolution, ISO 3611 typical accuracy of ±0.005 mm.
- Dasqua Depth Micrometer – Imperial — imperial equivalent, 0–4 inch or 0–6 inch range depending on rod set, 0.0001 inch resolution.
A dedicated depth micrometer guide is planned in the AIMS Mitutoyo Tier 2 article series.
Premium tier — Mitutoyo depth gauges via authorised supply chain
For toolroom work, inspection benches, CNC production where Mitutoyo accuracy and longevity justify the premium investment, AIMS supplies the full Mitutoyo depth gauge range through our authorised supply chain. The range covers:
- Mitutoyo Series 527 — vernier depth gauges, 0–150 mm to 0–1000 mm ranges
- Mitutoyo Series 547 ABSOLUTE Digimatic — compact, fine resolution (0.001 mm available), 5 µm base flatness, 3.5 year battery life, 0–200 mm range with extension rod sets
- Mitutoyo Series 571 ABSOLUTE Digimatic — long-range (up to 0–1000 mm), IP67 coolant-proof variants, hook-style models, electromagnetic induction ABSOLUTE encoder
- Mitutoyo Series 7211 — dial depth gauges with rack-and-pinion readout
- Mitutoyo Series 218 / 129 — depth gauges with interchangeable measuring rods for production work
- Mitutoyo Series 7210 — dial-type depth gauge for production environments preferring dial readout
Contact the AIMS team on (02) 9773 0122 or via the contact page for Mitutoyo depth gauge availability, model selection advice and quotation. Every Mitutoyo depth gauge supplied through AIMS comes through our authorised supply chain with the manufacturer warranty intact and the calibration inspection certificate included. Specify the model number where you know it; describe the application where you don't, and we will recommend the right Mitutoyo specification for the job.
Selection checklist by application
| Application | Recommended tool | Reasoning |
|---|---|---|
| Trade training, learning to read scales | Dasqua Vernier Depth Gauge 300 mm | Vernier teaches scale reading discipline. AIMS-stocked workshop tier at accessible price. Robust enough for student abuse |
| General fitting, layout work, occasional depth measurement | Maxigear Digital Depth Gauge | Fast read, mm/inch toggle, ABS/INC modes. AIMS-stocked workshop tier digital. Best general-purpose first depth gauge |
| Routine toolroom and inspection bench work, 0–200 mm range | Mitutoyo Series 547 ABSOLUTE Digimatic via authorised supply | Compact, fine resolution (0.001 mm available), 5 µm base flatness, ABSOLUTE encoder holds zero, lighter measuring force aids repeatability |
| CNC inspection bench with coolant exposure | Mitutoyo Series 571 ABSOLUTE Digimatic IP67 via authorised supply | IP67 coolant-proof, electromagnetic induction encoder unaffected by contamination. Long-range options available for larger work |
| Long-range depth measurement (300–1000 mm) | Mitutoyo Series 571 via authorised supply | Series 547 does not cover ranges above 200 mm. Series 571 is the only Mitutoyo digital depth gauge above 200 mm range |
| Tight-tolerance depth measurement (better than ±0.02 mm) | Depth micrometer — Dasqua online or Mitutoyo depth micrometer via authorised supply | Depth gauge accuracy hits a wall around ±0.02 mm. Depth micrometer (ISO 3611, ±0.005 mm typical) is the precision step-up |
| Production inspection — multi-shift, many operators | Mitutoyo Series 571 via authorised supply | Electromagnetic induction encoder has longer battery life and is unaffected by contamination. ABSOLUTE position retention through battery changes |
| Inspection-grade calibration lab — sub-micron resolution required | Mitutoyo Series 547 with 0.001 mm model via authorised supply | Finest resolution option in the Mitutoyo depth gauge line |
| Step height measurement from above the workpiece | Mitutoyo Series 571 hook-style via authorised supply | Hook attachment is the 571-specific feature for this application |
| Angled feature depth measurement, workshop-grade | Maxigear Angular Depth Gauge or Maxigear depth gauge protractor | Combination tools are workshop-tier. For inspection-grade angular depth use a precision angle plate plus a standard depth gauge |
| Field service / remote sites with reliable battery supply | Maxigear Digital Depth Gauge with spare batteries | Workshop-tier accuracy is fine for field work. Carry spare batteries |
| Field service / remote sites with unreliable battery supply | Dasqua Vernier Depth Gauge 300 mm | No battery dependency. Most robust of the depth gauge types |
| Tyre tread depth measurement (automotive) | Tyre tread depth gauge from automotive retail | Different product class. Workshop depth gauges are not the right tool. AIMS is not the right supplier — automotive retail is |
Depth gauge vs height gauge vs depth micrometer — when to use which
Three precision measurement instruments share the same workshop space and are often confused by buyers new to precision measurement. Each solves a distinct problem.
Depth gauge
Measures depth into a feature, with the workpiece surface itself as the reference plane. Base sits on the workpiece, rod descends into the hole or slot, gauge reads how deep the rod has dropped below the base. Used for counterbore depth, blind hole depth, slot and recess depth, step heights on shafts. Typical accuracy ±0.02 to ±0.05 mm depending on range and tier.
Height gauge
Measures height above the surface plate, with the surface plate as the absolute reference. Base sits on the surface plate, column rises vertically, measuring carriage records position above the plate. Used for layout scribing on the surface plate, dimensional inspection of workpiece features, comparative measurement against gauge blocks. Typical accuracy ±0.02 to ±0.06 mm depending on range. See our Height Gauge Guide for the deep-dive.
Depth micrometer
Measures depth like a depth gauge but with micrometer-grade accuracy. Uses interchangeable measuring rods to cover different depth ranges. Applies measuring force through a ratchet stop (5–10 N typical) rather than the lighter spring force of a depth gauge. Typical accuracy ±0.005 mm per ISO 3611 — about an order of magnitude tighter than a depth gauge. Used for tight-tolerance depth measurement: precision O-ring grooves, sealing surface recesses, critical counterbore depths on safety-critical joints.
The selection question
| If you need to measure... | Use this |
|---|---|
| Height above a surface plate (referenced from the plate) | Height gauge |
| Depth into a feature on a workpiece, ±0.02 mm tolerance acceptable | Depth gauge |
| Depth into a feature on a workpiece, ±0.005 mm tolerance required | Depth micrometer |
| Outside diameter, inside diameter, step difference on a workpiece | Caliper (vernier, dial or digital) — see our caliper guides |
| Very small features inaccessible to a depth gauge base | Caliper depth rod, accepting the accuracy compromise |
Frequently Asked Questions
How accurate is a depth gauge?
Under JIS B 7518:2018, a vernier or digital depth gauge with 0.02 mm scale interval is specified to a maximum permissible error of ±0.02 mm at measurement depths up to 50 mm, ±0.03 mm at 50–200 mm, ±0.04 mm at 200–400 mm, and ±0.05 mm at 400–500 mm. Gauges with the coarser 0.05 mm scale interval have wider MPE values. A premium Mitutoyo Series 547 ABSOLUTE Digimatic at 200 mm depth delivers ±0.02 mm. For tolerances tighter than this, step up to a depth micrometer specified to ±0.005 mm under ISO 3611. All accuracy specifications assume the gauge is calibrated, at 20 degrees Celsius reference temperature, and used with correct technique.
What is the difference between a depth gauge and a caliper depth rod?
A caliper depth rod is the thin rod extending from the back of a caliper's slider, designed for depth measurement as a secondary function. A dedicated depth gauge has a wide reference base that bridges across the workpiece surface, with a measuring rod that descends from the base. The wide base keeps measurement perpendicular to the reference surface by mechanical constraint — the caliper depends entirely on operator skill to hold it square. Practical Machinist consensus across many threads: caliper depth measurements are notoriously off without considerable practice. A 3-degree tilt error on a caliper depth rod introduces about 0.034 mm error on a 25 mm depth measurement — well past the caliper's specified accuracy. The dedicated depth gauge solves the problem with geometry, not operator skill.
What is the difference between Mitutoyo Series 547 and Series 571?
The Series 547 is Mitutoyo's compact ABSOLUTE Digimatic depth gauge — 0–200 mm range, finest available resolution (0.001 mm option), 5 µm base flatness, 1.4 N measuring force, 3.5 year battery life. Best for toolroom, inspection bench and general workshop in dry environments. The Series 571 is Mitutoyo's long-range, environmentally hardened ABSOLUTE Digimatic depth gauge — ranges from 0–150 mm up to 0–1000 mm, 0.01 mm resolution only, IP67 coolant-proof variants available, hook-style models for step measurement, electromagnetic induction ABSOLUTE encoder. Best for CNC inspection in coolant-exposed environments, long-range fabrication work, and production where the encoder must hold zero through power cycles. Specifying the wrong series is the most common Mitutoyo depth gauge purchase error.
What is the Mitutoyo ABSOLUTE encoder?
The Mitutoyo ABSOLUTE encoder is a patent-protected electromagnetic induction position measurement technology (US Patents 8,847,583 B2 and 8,928,311 B2) used across Mitutoyo's precision measuring product line. Unlike standard capacitive encoders, it uses electromagnetic induction between transmitter and receiver coils through a precision scale coil pattern. The technical differentiators: (1) the instrument knows its absolute position the moment power is applied, with no reference drive required; (2) the encoder is unaffected by coolant, swarf or dust contamination that disrupts capacitive encoders; (3) battery life is years rather than months because the encoder draws minimal current; (4) the calibrated origin point is retained for the life of the battery. This is the technology that justifies the premium tier price for Mitutoyo ABSOLUTE instruments.
How do you use a depth gauge correctly?
Clean the workpiece reference surface and the gauge base — dust particles are bigger than the gauge's accuracy specification. Remove burrs around the feature being measured. Release the locking screw, place the gauge base flat across the workpiece surface centred over the feature, and lower the rod gently until it touches the feature bottom. Use the fine-feed for the final approach — heavy finger pressure on the rod gives shallow readings. Confirm firm but not heavy contact. Lock the rod. Lift the gauge clear of the workpiece and read. Use two-handed technique: hold the base with one hand on the workpiece while manipulating the rod with the other. One-handed operation cannot maintain square reference. Confirm the reading repeats before recording — a reading that doesn't repeat hasn't been taken correctly.
How do you measure counterbore depth?
A counterbore must be deep enough for the fastener head to sit flush or slightly below the workpiece surface. Place the depth gauge base flat across the workpiece surface around the counterbore. Lower the rod into the counterbore until it contacts the flat bottom. Avoid placing the rod tip on the corner radius between the bore wall and the bottom — that gives a false 'not deep enough' reading because the rod is supported on the radius rather than the flat. Move the rod laterally within the counterbore to confirm it sits on the true flat bottom. Lock the rod, lift the gauge clear, and read the depth. Counterbore depth tolerance is typically ±0.1 mm or tighter, well within workshop-tier digital depth gauge specification.
How do you measure blind hole depth without trapped air?
Blind holes can trap cutting fluid or air at the bottom, preventing the rod from reaching the actual feature bottom. The gauge then reads false shallow. Blow compressed air into the hole before measurement to clear cutting fluid and chips. Tip the workpiece if orientation allows trapped air to escape. On precision inspection work, measure twice with the part oriented differently between measurements — if readings disagree, trapped fluid or air is the likely cause. For very critical measurements use a depth micrometer with a needle-tip rod that can penetrate a small fluid layer. The trapped-air problem is most acute on close-tolerance blind holes where there is minimal clearance between the rod and the hole wall for air to escape.
What is JIS B 7518?
JIS B 7518 is the Japanese Industrial Standard for vernier, dial and digital depth gauges — the de facto global reference standard for depth gauge specifications. The current edition is JIS B 7518:2023, which superseded JIS B 7518:2018. The standard sets maximum permissible errors (MPE) by measurement depth and scale interval, design and metrological requirements for the base, rod, scale and readout, and calibration guidelines. Mitutoyo helped develop the standard and most depth gauges sold globally cite JIS B 7518 compliance. The international equivalent is ISO 13225:2012 (which covers caliper depth gauges and height gauges among other dimensional measuring equipment). There is no Australian Standard specific to depth gauges — AU industry uses JIS B 7518 and ISO 13225 as the reference.
How often should a depth gauge be calibrated?
Cadence depends on use intensity. High-use production lines: every 6 to 12 months. Inspection-grade tools subject to ISO 9001 quality systems: annually minimum, with NATA-accredited calibration certificate. Routine workshop use: annually. Hobby or low-volume use: every 2 to 5 years, or whenever the gauge has been dropped or shows visible damage. Replaceable-rod gauges (Mitutoyo Series 218, Starrett rod sets): must be calibrated each time the rods are reassembled, set against gauge blocks to the major ranges of each rod. Digital gauges in coolant or harsh environments need more frequent checks because encoder drift and IP seal degradation are accelerated. The calibration certificate should state measurement uncertainty at each tested point and reference the calibration laboratory's NATA accreditation.
Can I use a caliper depth rod instead of a depth gauge?
For occasional measurements, quick approximate checks, and features too narrow for a depth gauge base to span (smaller than about 4 mm), the caliper depth rod is acceptable. For routine depth measurement, inspection-grade work, critical depth dimensions (counterbore for fastener seating, blind hole for thread engagement, O-ring grooves), CNC setup verification, or any measurement where the dimensional tolerance is tight, a dedicated depth gauge gives substantially better repeatability. The geometry of the wide base enforces square measurement that a narrow caliper cannot guarantee. Practical Machinist consensus: caliper depth measurements are 'ok but not great' compared to dedicated depth gauge measurements.
Why is my depth gauge reading inconsistent?
Inconsistent readings usually trace to one of several causes. Dirty base or dirty workpiece surface — wipe both before measurement. Burrs around the feature being measured — deburr first. Heavy finger pressure on the rod flexing it — use the fine-feed for final approach. One-handed operation tilting the gauge — switch to two-handed technique. Rod tip on a radius rather than the flat bottom — move the rod laterally to find the true low point. Half-base hanging off the workpiece edge — set up with the base fully supported. Trapped fluid or air on a blind hole — blow out before measurement. A damaged or bent rod from a previous drop — inspect for straightness and run a calibration check against gauge blocks. If none of these resolves the inconsistency, the gauge needs service or replacement.
How do I spot a fake Mitutoyo depth gauge?
Run the five-check spot-the-fake procedure. First, rod fit and feel — genuine Mitutoyo rod slides smoothly with no lateral wobble; fakes have visible slop. Second, fine-feed knob feel — genuine has a smooth glass-like feel; fakes feel gritty. Third, 'Made in Japan' marking on the case underside — genuine has moulded text; fakes have no marking or a peelable sticker. Fourth, base flatness and finish — genuine has Mitutoyo satin-chrome and sits without rocking on a flat reference (Series 547 specifies 5 µm base flatness); fakes have duller finish and may rock. Fifth, serial number quality — genuine is crisply etched in the correct Mitutoyo font; fakes are fuzzy or off-centre. Also confirm spelling is exactly 'Mitutoyo' — variants like 'Mitutogo', 'MITU-tyo' or 'Mituttoyo' are counterfeits. Documentation check: genuine ships with Mitutoyo calibration inspection certificate with traceable serial number; counterfeits ship with no documentation or photocopies.
What size depth gauge should I buy?
For most Australian workshops, a 0–150 mm range is the default first purchase. It covers most fastener counterbore, slot depth, step measurement and general fitting work. A 0–300 mm range — the Dasqua Vernier Depth Gauge 300 mm stocked at AIMS — is the next step up for larger fabrication. A 0–600 mm range is specialty equipment for very large work, almost exclusively a Mitutoyo Series 571 purchase. A 0–1000 mm range is industrial fabrication and large structural work, again Series 571 territory. Going larger than you need adds weight and bulk without benefit, and magnifies any thermal effects on accuracy.
What is the difference between a depth gauge and a depth micrometer?
Both measure depth, but with different accuracy classes and applications. A depth gauge uses a sliding rod with vernier, dial or digital readout. Typical accuracy is ±0.02 mm for workshop-tier digital at moderate ranges. A depth micrometer uses interchangeable rods of fixed lengths combined with a micrometer head. ISO 3611 specifies depth micrometers to ±0.005 mm over a 25 mm rod range — about an order of magnitude tighter than a depth gauge. The depth micrometer applies measuring force through a ratchet stop (5–10 N) rather than the lighter spring force of a depth gauge (1.4 N on Mitutoyo Series 547). Depth micrometers are the precision step-up for tight-tolerance depth measurement: precision O-ring grooves, sealing surface recesses, critical counterbore depths.
What is layout dye and does it apply to depth gauges?
Layout dye (Dykem or similar) is a fast-drying coloured marking fluid used with height gauges and surface gauges to make scribed lines visible. It is not directly relevant to depth gauge measurement because a depth gauge does not scribe lines — it measures depths. However, if you are setting up a workpiece for combined height-gauge layout work and depth-gauge inspection (common on toolroom one-off parts), the layout dye will be applied during the height gauge stage and the depth gauge will be used afterward to verify the actual machined depths against the scribed layout reference. See our Height Gauge Guide for the layout dye application detail.
AIMS depth gauges — quick links and contact
Browse the AIMS measuring tools collection for current stocked precision measuring equipment including the Dasqua Vernier Depth Gauge 300 mm, Maxigear Digital Depth Gauge, Dasqua depth micrometers (metric and imperial) and Maxigear angular depth gauge protractor combination tools. For Mitutoyo Series 527 vernier, Series 547 ABSOLUTE Digimatic, Series 571 long-range and IP67 variants, Series 7211 dial and Series 218 / 129 / 7210 interchangeable-rod and dial-type depth gauges sourced through our authorised supply chain, contact the AIMS team on (02) 9773 0122 or via the contact page — let us know the Mitutoyo model number or describe the application, and we will quote with current availability and lead time. Every Mitutoyo depth gauge supplied through AIMS comes with the manufacturer warranty and calibration certificate intact.
Related AIMS guides: Vernier Caliper Guide · Digital Caliper Guide · Dial Caliper Guide · Height Gauge Guide · Micrometer Guide · Dial Indicator Guide · GD&T Symbols Guide
For tap selection by hole type and material, see our Tap Types Explained guide.
