A shoulder bolt is a precision fastener with three distinct zones along its shank: a cylindrical head, an unthreaded precision shoulder, and a threaded section with a smaller diameter than the shoulder. It is this three-zone geometry that separates a shoulder bolt from every other fastener type and makes it the correct choice for applications where a rotating, pivoting, or sliding fit between mating components is required.
Shoulder bolts are also called shoulder screws and, in tooling and die work, stripper bolts — all three terms describe the same component. This guide covers how shoulder bolts work, how to specify them correctly, ISO 7379 dimensions and tolerances, material options, application types, clearance hole selection, and installation practice.
Browse the AIMS fastener range for shoulder bolts and related products, or read on for the full technical guide.
What Is a Shoulder Bolt?
A shoulder bolt is a machine screw with an enlarged, unthreaded cylindrical section — the shoulder — between the head and the thread. The shoulder diameter is always larger than the thread diameter, and it is the shoulder, not the thread, that performs the primary mechanical function in most applications.
The three terms used interchangeably in Australian industry are:
- Shoulder bolt — the general engineering term, used across most industries
- Shoulder screw — an equally common alternative; no functional difference from "shoulder bolt"
- Stripper bolt — the same component, named for its specific use in punch-and-die tooling where it retains and guides the stripper plate. You will also occasionally hear "puller bolt" in the same context.
The confusion between "bolt" and "screw" is longstanding in Australian fastener supply. In practice, shoulder bolts typically thread directly into a tapped hole in one of the mating components — making them technically a screw by the strictest definition — but "shoulder bolt" is the term most commonly used in engineering and procurement. Either term will be understood by any fastener supplier or engineer.
What a shoulder bolt is not: it is not a standard socket cap screw with a reduced-diameter shank, and it is not a bolt designed primarily to clamp two parts together. Its purpose is to provide a precision cylindrical surface — the shoulder — that acts as a shaft, axle, pivot, or linear guide, while the threaded section anchors it in place.
Anatomy of a Shoulder Bolt: Three Zones
Understanding the three zones of a shoulder bolt is essential to specifying and applying them correctly.
Zone 1 — The Head
The standard head form for shoulder bolts per ISO 7379 is a socket head cap screw style — a cylindrical head with a hexagon socket (Allen key) drive. The head diameter is larger than the shoulder, providing a bearing face that retains the assembled component against axial movement in one direction. Low-profile head variants are available for installations where overall stack height is constrained.
The head does not clamp the mating components together in the way a standard bolt head does. In most shoulder bolt applications, a clearance exists between the underside of the head and the face of the component, allowing the mating component to rotate or slide freely on the shoulder without the head bearing on it.
Zone 2 — The Shoulder
The shoulder is the precision-ground, unthreaded cylindrical section that forms the working element of the fastener. It is specified by two dimensions: shoulder diameter (d) and shoulder length (L). These are the primary sizing dimensions for a shoulder bolt — not the thread size.
The shoulder is ground to a tight diameter tolerance — typically h6 per ISO 7379, which for a 10 mm shoulder means a tolerance band of approximately −0.009 mm to 0 mm (i.e., the shoulder is up to 9 µm undersize but never oversize). This h6 tolerance provides a smooth, reliable running fit in an H7-tolerance clearance hole, which is the standard pairing for shoulder bolt applications.
The shoulder surface finish is Ra ≤ 0.8 µm per ISO 7379 — smooth enough to act as a bearing journal surface directly, without a sleeve or liner, in many low-speed pivot and guide applications.
Zone 3 — The Thread
The threaded section is always smaller in diameter than the shoulder. It threads into a tapped hole in the component being fastened, anchoring the shoulder bolt in position. The thread is metric coarse (e.g., M5, M6, M8, M10, M12) with a 5g6g tolerance class per ISO 7379.
An important consequence of the thread being smaller than the shoulder: the thread has a reduced cross-sectional area relative to the shoulder diameter, which means the tensile and torsional strength of the threaded section is limited compared to a full-size socket cap screw of the same head size. Shoulder bolts should not be overtightened — see the installation section below.
The thread length is standardised relative to the thread diameter, not the shoulder length, and is typically 1.0–1.5× the thread diameter. This is usually sufficient to anchor the bolt securely in the tapped hole without the threads bottoming out.
How a Shoulder Bolt Differs from a Standard Socket Cap Screw
The easiest way to understand a shoulder bolt is to compare it directly to a standard socket cap screw (SHCS), which is the fastener most commonly confused with it in procurement.
| Feature | Socket Cap Screw (SHCS) | Shoulder Bolt |
|---|---|---|
| Shank | Fully threaded, or threaded to near the head | Unthreaded precision shoulder + short thread at tip |
| Thread vs shank diameter | Thread = shank diameter | Thread < shoulder diameter (always) |
| Primary function | Clamp two or more parts together in tension | Provide a precision shaft, pivot, or guide surface |
| Hole in mating part | Clearance hole sized to thread OD | Clearance hole sized to shoulder diameter (H7 typical) |
| Tolerance | Commercial (relatively loose) | Precision ground — h6 shoulder tolerance per ISO 7379 |
| Surface finish | Standard | Ground — Ra ≤ 0.8 µm on shoulder |
| Size specification | Thread size (e.g., M8 × 30) | Shoulder diameter × shoulder length (e.g., 10 mm × 50 mm) |
| Rotating fit | Not suitable — thread creates misalignment and fretting | Designed for — shoulder h6/H7 pairing gives clean running fit |
The most common error in shoulder bolt applications is substituting a standard SHCS and relying on its unthreaded shank (the portion between head and thread start) as the bearing surface. An SHCS shank is not ground to a tight tolerance, is not a designed bearing surface, and will not provide the consistent clearance and surface finish required for reliable rotating or sliding operation.
Shoulder Bolt Standard: ISO 7379
The governing standard for metric shoulder bolts in Australia is ISO 7379, which specifies hexagon socket head shoulder screws in metric dimensions. Key technical provisions of ISO 7379:
Shoulder Diameter Tolerance
h6 — tight, ground tolerance. The shoulder is slightly undersize relative to nominal diameter, never oversize. This pairs with an H7 hole in the mating component to give an H7/h6 running clearance fit.
Thread Tolerance
5g6g — the standard close-tolerance thread for precision fasteners. This provides accurate thread positioning in the tapped hole.
Property Class
ISO 7379 specifies property class 12.9 for steel shoulder bolts. Class 12.9 has a minimum tensile strength of 1,220 MPa. There is an important marking convention: class 12.9 shoulder bolts are marked 012.9 (with a leading zero), not 12.9 — the leading zero indicates reduced loadability, reflecting the fact that the small threaded section limits overall fastener strength below what the 12.9 marking alone would imply.
Surface Finish
Shoulder surface: Ra ≤ 0.8 µm. This is a functional finish requirement that ensures the shoulder can serve as a bearing journal surface.
Dimensional Relationship: Shoulder to Thread
ISO 7379 defines standardised pairings between shoulder diameter and thread size. The thread is always one or two sizes smaller than the shoulder:
| Shoulder diameter (mm) | Thread (metric) | Socket size (mm) |
|---|---|---|
| 4 | M3 | 2.5 |
| 5 | M4 | 3 |
| 6 | M5 | 4 |
| 8 | M6 | 5 |
| 10 | M8 | 6 |
| 12 | M10 | 8 |
| 16 | M12 | 10 |
| 20 | M16 | 14 |
| 25 | M20 | 17 |
This table is critical for correct hole specification and tap selection. When someone orders a "10 mm shoulder bolt," the hole in the rotating or sliding part must be 10 mm (H7 tolerance), and the tapped hole in the base component is M8 — not M10.
How Shoulder Bolts Are Sized
A shoulder bolt is sized by shoulder diameter and shoulder length — not by thread size. This is one of the most common points of confusion in procurement.
A shoulder bolt described as "10 mm × 50 mm" has a shoulder diameter of 10 mm and a shoulder length of 50 mm. The thread is M8 (as per the ISO 7379 table above). The thread length is additional to the shoulder length and is not included in the 50 mm dimension.
When specifying a shoulder bolt, you need:
- Shoulder diameter — determines the bore size of the rotating or sliding component, and the tap size in the base
- Shoulder length — must match (or slightly exceed) the thickness of the component that sits on the shoulder; too short and the head clamps the component, preventing rotation; too long and the component has axial float
- Material / finish — Grade 12.9 alloy steel (standard), stainless steel A2 or A4, or black oxide for specific environments
- Head style — socket head (standard per ISO 7379), low profile, or countersunk for flush installations
Shoulder Length vs Component Thickness
The shoulder length must be carefully matched to the component stack it supports. The shoulder length should be equal to or very slightly greater (typically 0.1–0.3 mm) than the total thickness of the component(s) that sit on it and must be free to rotate or slide. If the shoulder is too short, the head clamps the component against the base, preventing movement. If too long, the component has axial play that may cause noise, wear, or mis-indexing.
For spring-loaded assemblies where the shoulder bolt acts as a travel limiter (common in stripper bolt die applications), the shoulder length is designed to be longer than the component stack by the desired travel distance, allowing the component to move axially along the shoulder before the head bottoms out.
Shoulder Bolt Applications
Shoulder bolts perform four fundamental mechanical functions: pivot, linear guide, bearing shaft, and travel stop. Most real-world applications combine two or more of these.
Pivot Points and Rotating Assemblies
The most common general-purpose application. A shoulder bolt provides a precision pivot for lever arms, linkages, cam followers, rollers, pulleys, and any component that needs to rotate about a fixed axis. The mating component has a bore sized to the shoulder diameter (H7 tolerance), which provides a clean running fit. The shoulder bolt threads into the base structure and is tightened to retain position — the mating component is free to rotate on the shoulder.
This application is common across maintenance and machinery engineering: jig and fixture pivots, hinged guards, tensioner arms, belt idler rollers, linkage pins, and similar. The advantage over a pin-and-circlip arrangement is that the shoulder bolt is self-retaining without additional hardware, and the precision shoulder diameter provides better alignment accuracy than a plain dowel pin secured by other means.
Linear Slides and Guide Pins
Where a component must slide along a fixed axis — rather than rotate — the shoulder bolt acts as a guide pin. The mating component has a slot or elongated hole that engages the shoulder, constraining it laterally while allowing axial movement. The shoulder provides a ground bearing surface for the slot to run against without wear of the bolt threads.
This application appears in adjustable mounting brackets, clamping fixtures, tool slide mechanisms, and anywhere an elongated slot-and-guide arrangement is required. The precision h6 shoulder diameter ensures consistent clearance in the H7 slot and prevents wobble.
Bearing Shafts
The shoulder can serve directly as the inner shaft of a needle roller bearing, plain bush, or similar bearing element. When a rolling element bearing is mounted on the shoulder, the shoulder diameter is sized to match the bearing bore, and the shoulder length is sized so that the head bears against the inner race face — fixing the inner race axially while the outer race is free to rotate within its housing.
The h6 shoulder tolerance provides a suitable running clearance for most plain bush applications and a light interference or transition fit (depending on the actual finished diameter within the h6 band) for inner race mounting. For precision bearing work, check the actual measured shoulder diameter against the bearing manufacturer's shaft tolerance recommendation — do not assume h6 always provides the intended fit for every bearing inner race.
Stripper Bolts in Punch Dies and Injection Moulds
The "stripper bolt" name comes from this application. In progressive die stamping, a stripper plate is held against the die face by a set of shoulder bolts threaded into the die block. During press operation, the stripper plate travels axially along the shoulders — compressing a spring stack — then returns. The shoulder provides the precision guide surface for the stripper plate motion, and the shoulder length (plus spring pre-load) determines the stripping stroke.
In injection moulding, shoulder bolts perform a similar function in ejector assemblies and side-action mechanisms — guiding mould components that must move axially during the opening and ejection cycle, with the shoulder bolt head acting as a positive stop at the end of travel.
In both applications, the fit between shoulder and guide bore is critical. Excessive clearance causes plate wobble and misalignment; insufficient clearance causes binding and galling. The standard H7/h6 fit is appropriate for most tool-room applications. Very high-speed presses may require tighter fits or hardened shoulder bolts.
Spring-Loaded Travel Limiting
In spring-loaded assemblies — clamping mechanisms, pressure pads, floating supports — shoulder bolts are used as captive travel limiters. The shoulder bolt passes through a clearance hole in the floating component and threads into the base. The floating component sits on a spring, and the shoulder bolt head limits its travel when the spring extends. The shoulder length minus the component bore depth determines the maximum travel distance.
This application is common in workholding fixtures, die sets, and spring-loaded contact pads. The precision shoulder diameter is less critical here than in rotating applications — the shoulder just needs to pass cleanly through the clearance hole — but the shoulder length tolerance directly affects assembly travel and must be specified carefully.
Shoulder Bolt Materials and Finishes
Grade 12.9 Alloy Steel — Plain or Black Oxide
The standard material for shoulder bolts per ISO 7379. Grade 12.9 alloy steel provides the highest strength and the best dimensional consistency for precision applications. Plain (bright) finish is standard. Black oxide (blackened) finish provides marginal corrosion resistance and is common for toolroom and die-set applications — it does not substantially alter shoulder diameter and preserves the h6 tolerance.
Grade 12.9 shoulder bolts are not suitable for corrosive or food-grade environments — the alloy steel will rust if exposed to moisture without protective coating.
Stainless Steel — A2 and A4
A2 stainless (304) and A4 stainless (316) shoulder bolts are available for corrosion-resistant applications: food processing equipment, marine and wash-down environments, chemical handling, and outdoor installations. The trade-off: stainless shoulder bolts are softer than Grade 12.9 steel (A2/A4 property class 70 = 700 MPa tensile strength vs 1,220 MPa for 12.9), meaning they carry lower torque and shear loads and are more susceptible to galling — particularly in sliding contact applications. Anti-galling precautions (anti-seize compound, dissimilar material pairing) should be considered for stainless shoulder bolts in sliding guide applications.
Stainless shoulder bolts may not be precision-ground to the same h6 tolerance as Grade 12.9 steel — verify with the supplier before specifying for precision fits.
Titanium and Other Alloys
Titanium shoulder bolts are available for aerospace and high-performance applications requiring low weight with acceptable strength. These are specialty items, not general stock, and will be sourced to order.
Shoulder Bolt Sizes: Standard Metric Range
Australian industrial supply typically covers the metric range per ISO 7379 from M3 thread (4 mm shoulder) through to M16 thread (20 mm shoulder), with shoulder lengths from approximately 5 mm to 100 mm depending on diameter. The most commonly stocked sizes in Australian industrial supply are M5 through M12 thread (6 mm through 16 mm shoulder diameter).
| Shoulder diameter (mm) | Thread | Typical shoulder length range (mm) | Common application range |
|---|---|---|---|
| 4 | M3 | 5–30 | Miniature mechanisms, electronics tooling |
| 5 | M4 | 5–40 | Light-duty pivots, precision fixtures |
| 6 | M5 | 5–50 | Jig work, light linkages |
| 8 | M6 | 8–60 | General pivots, small die sets |
| 10 | M8 | 10–80 | General industrial pivots, stripper bolts, cam followers |
| 12 | M10 | 12–80 | Medium die sets, bearing shafts, conveyor pivots |
| 16 | M12 | 16–100 | Heavy-duty pivots, larger die sets, roller axles |
| 20 | M16 | 20–100 | Heavy machinery linkages, large tooling |
The M6 thread (8 mm shoulder) and M8 thread (10 mm shoulder) sizes are the most frequently ordered in general Australian industrial supply — they cover the majority of jig, fixture, and light machinery pivot and guide applications. For die and moulding tooling, M8–M12 thread sizes (10–16 mm shoulder) dominate.
Standard shoulder length increments vary by supplier and diameter. Common increments are 5 mm steps for small sizes and 10 mm steps for larger diameters. If a non-standard shoulder length is required, the options are: ordering a longer standard size and machining the shoulder to length (shoulder bolts can be turned to length in a lathe), or ordering a custom-length fastener to specification.
Clearance Hole and Fit Selection
The mating hole — the bore in the component that sits on the shoulder — must be sized correctly for the intended application.
Standard Fit: H7/h6
The standard pairing for shoulder bolt applications is an H7 hole tolerance mating with the h6 shoulder. This gives a clearance fit with approximately 0.010–0.034 mm total clearance for a 10 mm diameter shoulder (the exact range depends on the position within both tolerance bands). This is sufficient clearance for:
- Low-to-moderate speed rotation (e.g., pivots, cam followers, roller axles)
- Smooth linear sliding (e.g., stripper plates, guide pins, adjustable brackets)
- Manual or slow-speed mechanisms
For an H7 hole on a 10 mm shoulder: upper deviation +0.015 mm, lower deviation 0. Drill to 10 mm and ream to 10H7. A standard 10 mm drill will typically be a few hundredths undersize — always finish with a reamer when precision fits are required. Drilling to size without reaming produces a hole that is slightly out-of-round and with a rougher surface finish than necessary for precision fits.
Clearance Holes for Non-Precision Passes
Where the shoulder bolt passes through a component that does not bear on the shoulder (e.g., a cover plate, a spacer, or a non-bearing through-passage), use a standard clearance hole — typically shoulder diameter + 0.3 to 0.5 mm. This allows easy assembly without requiring precision alignment of the hole to the shoulder. Do not use H7 clearance holes for non-bearing passes — they make assembly unnecessarily difficult and may cause the shoulder to bear against the hole wall even in non-functional positions.
Axial Clearance at the Shoulder End
The end of the shoulder must not bottom out against the tapped hole face. A clearance of at least 0.5–1 mm between the shoulder end face and the start of the thread (the undercut or runout) must be maintained. ISO 7379 specifies a defined thread run-out at the base of the shoulder. When specifying shoulder length, ensure this clearance is preserved — if the shoulder bottoms before the thread is fully engaged, the bolt cannot be properly tightened.
Installation and Common Mistakes
Correct Installation Sequence
To install a shoulder bolt correctly:
- Confirm the tapped hole is the correct thread size (per the ISO 7379 table — the thread is one or two sizes smaller than the shoulder) and has the correct depth (at least 1.5× thread diameter).
- Confirm the clearance bore in the mating component is reamed to H7 (or the appropriate tolerance for the application).
- Apply a small amount of medium-strength thread locking compound (e.g., Loctite 243) to the thread if the assembly is subject to vibration, or use dry threads if the bolt may need regular removal.
- Start the thread by hand to ensure it engages squarely. Shoulder bolts have relatively fine threads — cross-threading will damage the tapped hole.
- Tighten with the correct Allen key — typically 4–6 mm for M6–M8 thread sizes. Tighten to the manufacturer's specified torque, or apply moderate hand torque only. Do not apply the same torque you would use for a standard socket cap screw of the same head size.
- Confirm the mating component rotates or slides freely after installation. If it is tight, the shoulder is too short (head is clamping the component) or the bore is undersized.
Do Not Overtighten
The single most common installation mistake is overtightening. The head of a shoulder bolt looks identical to a standard socket cap screw head of a larger size — an M8-thread shoulder bolt (10 mm shoulder) has a similar head to a standard M10 or M12 cap screw. Technicians unfamiliar with shoulder bolts may apply the torque appropriate for the head size, not the thread size, snapping the thread or yielding the underhead bearing face.
ISO 7379 explicitly notes that the maximum tightening torque is not determined by the 12.9 property class but by the relatively small bearing area of the shoulder face and the reduced cross-section at the shoulder-to-thread transition. Tighten until the head is snug against the component face (or spacer), not until the component is clamped.
Correct Shoulder Length is Critical
If the shoulder is too short for the mating component stack, the head will clamp the component and prevent rotation or sliding — the most common cause of a "binding" shoulder bolt assembly. If the shoulder is too long, the component will have unintended axial float. Measure the thickness of the mating component or component stack accurately before ordering shoulder length.
Thread Locking for Vibration Applications
Shoulder bolts in vibrating machinery — conveyor drives, compressors, punch presses — should be secured with thread locker. The small thread has limited friction-based self-locking capacity. A single drop of medium-strength locking compound (e.g., Loctite 243) is sufficient. Do not use high-strength compound (e.g., Loctite 270) if the bolt may need removal for component maintenance — you may not be able to break it out without damaging the tapped hole.
Avoid Lateral Overloading
Shoulder bolts can handle significant shear loads — the shoulder transmits shear directly, not through the thread — but the relatively small thread section at the end of a long shoulder creates a cantilever, and lateral (bending) loads on long-shoulder, small-thread bolts can cause fatigue failure at the shoulder-to-thread transition. For applications with significant lateral or bending loads, use the shortest shoulder length that meets the application requirement, and consider whether a press-fit pin or a larger diameter fastener is more appropriate.
Shoulder Bolt vs Dowel Pin: When to Use Which
Shoulder bolts and dowel pins both provide precision cylindrical surfaces for locating, pivoting, and guiding, and the two are occasionally confused in design. The decision comes down to how the component is retained:
| Shoulder bolt | Dowel pin | |
|---|---|---|
| Self-retaining? | Yes — threaded end anchors the bolt in place | No — requires separate retention (press fit, end cap, circlip) |
| Adjustable axial position? | No — fixed by thread depth and shoulder length | Yes — can be pressed to any depth within the hole |
| Rotating application? | Suitable — h6/H7 running fit | Suitable if press-fit into one part, clearance in the other |
| Removal/serviceability | Easy — hex socket, tool-removable | Requires pin punch or press; can be difficult if seized |
| Travel limiting | Yes — head acts as positive stop | No — separate feature required |
In general: if the pivot or guide element needs to be tool-removable for maintenance, and if the head-as-stop feature is useful, choose a shoulder bolt. If the pin must be flush-mounted, or the retention method is not thread-based, a dowel pin or roll pin may be more appropriate. See the AIMS Roll Pin Guide for roll pin applications and selection.
AIMS Shoulder Bolt Range
AIMS stocks Grade 12.9 socket head shoulder bolts in the standard ISO 7379 metric range — shoulder diameters from 6 mm to 20 mm, stainless steel A2 options in common sizes, and black oxide Grade 12.9 for toolroom applications. Standard shoulder lengths in 5–10 mm increments are available from Sydney warehouse stock.
Browse the AIMS fastener range for current stock and pricing, or call the team on (02) 9773 0122 or contact us online for sizing assistance, non-standard shoulder lengths, or advice on application fit and material selection.
For related fastener guides, see the Socket Head Cap Screw Guide, the Roll Pin Guide, and the Metric Bolt Torque Chart.
Frequently Asked Questions
What is a shoulder bolt used for?
A shoulder bolt provides a precision cylindrical shaft — the shoulder — that acts as a pivot, axle, linear guide, or bearing surface. Common applications include pivot points in lever and linkage assemblies, guide pins in punch dies and injection moulds (where they are also called stripper bolts), bearing shafts for cam followers and rollers, and travel limiters in spring-loaded assemblies. The shoulder is the working element; the thread simply anchors it in place.
What is the difference between a shoulder bolt and a shoulder screw?
There is no functional difference — the terms are interchangeable. Both describe the same fastener: a precision socket head fastener with an unthreaded shoulder between the head and a smaller threaded section. "Shoulder bolt" is more common in Australian general engineering; "shoulder screw" is equally used in precision and toolroom contexts. "Stripper bolt" is the same component used specifically in punch die and injection mould applications.
How do I specify the size of a shoulder bolt?
Shoulder bolts are specified by shoulder diameter and shoulder length — not by thread size. For example, "10 mm × 50 mm shoulder bolt" means the shoulder is 10 mm in diameter and 50 mm long. The thread is M8 (per ISO 7379 — one size down from the 10 mm shoulder). Always specify shoulder diameter first, then shoulder length, then material and finish. Do not specify thread size as the primary dimension — suppliers will ask for shoulder diameter anyway.
What size hole do I drill for a shoulder bolt?
The hole in the rotating or sliding component must match the shoulder diameter, finished to H7 tolerance. Drill to nominal diameter and finish with a reamer — do not rely on a drill to give a precise enough finish for shoulder bolt fits. For a 10 mm shoulder bolt, drill and ream to 10H7 (+0.015/0 mm). The tapped hole in the base must match the thread size (M8 for a 10 mm shoulder), not the shoulder diameter. Never tap to the shoulder diameter.
Why is the thread on a shoulder bolt smaller than the shoulder?
This is the fundamental design intent. The shoulder must be free to pass through the bore in the mating component (with running clearance) while the thread engages only the base component. If the thread were the same diameter as the shoulder, the mating component would have no clearance distinction between the shoulder zone and the thread zone. The smaller thread also means the mating component can be removed by backing the bolt out, with the shoulder sliding freely through the bore as the thread disengages.
Can I use a shoulder bolt as a regular bolt?
Technically yes, but it is the wrong tool for the job and is wasteful. A shoulder bolt is more expensive than a standard socket cap screw due to its precision ground shoulder and tight tolerances. Using one where a standard SHCS would suffice adds unnecessary cost. Conversely, using a standard SHCS where a shoulder bolt is required — to save cost — will not provide the precision fit and surface finish needed for rotating or sliding applications, and the assembly will wear rapidly or bind.
What is a stripper bolt?
A stripper bolt is a shoulder bolt used in punch-and-die stamping or injection mould tooling to retain and guide the stripper plate. The shoulder bolt threads into the die block, and the stripper plate slides along the shoulder as the press cycles — the shoulder provides the precision guide surface, and the bolt head is the positive stop at end of travel. The name derives from the "stripping" action of the plate that strips the workpiece from the punch after each stroke. Functionally and dimensionally, a stripper bolt is identical to any other shoulder bolt; the name is purely application-specific.
What grade are shoulder bolts?
Standard metric shoulder bolts per ISO 7379 are Grade 12.9 alloy steel — the highest commercial fastener grade, with minimum tensile strength of 1,220 MPa. Note: Grade 12.9 shoulder bolts are marked "012.9" (with a leading zero) to indicate reduced loadability due to the small thread section relative to the head size. Stainless steel shoulder bolts (A2 or A4) are Grade 70 (700 MPa tensile) — significantly lower strength than 12.9 steel. The material choice affects maximum load, not the precision of the shoulder.
Do shoulder bolts need locking compound?
In vibrating machinery, yes. The small threaded section has limited self-locking friction and can back out under vibration. A single drop of medium-strength thread locker (Loctite 243 or equivalent) is sufficient. Do not use high-strength compound if the bolt needs to be removable for maintenance. In static or low-vibration applications, locking compound is optional but adds insurance against loosening, particularly in accessible locations where inadvertent contact might loosen the bolt.
What is the clearance between a shoulder bolt and the hole?
For a standard H7/h6 fit pairing, the total clearance is approximately 0.010–0.034 mm for a 10 mm shoulder diameter. This is sufficient for smooth rotation and sliding in most industrial applications. For very high precision work, check the actual measured shoulder diameter (within the h6 tolerance band) against your hole tolerance to confirm the fit class you are achieving. Commercial-grade shoulder bolts from some suppliers may not achieve the full h6 tolerance — check the manufacturer's specification.
Can a shoulder bolt be used with a needle roller bearing?
Yes — this is a common application. The shoulder bolt acts as the inner race shaft for the needle roller bearing (e.g., a cam follower or yoke-type roller). The shoulder diameter is sized to match the bearing bore, and the shoulder length is set so the bolt head bears on the inner ring face. The outer ring of the bearing runs in its housing. The h6 shoulder tolerance typically gives a suitable shaft fit for most needle roller and drawn cup roller bearing bores — verify against the bearing manufacturer's recommended shaft tolerance for the specific bearing type and load direction.
How long should a shoulder bolt be?
The shoulder length must equal or very slightly exceed (by 0.1–0.3 mm) the thickness of the component(s) that sit on the shoulder and must move freely. If shorter, the head clamps the component and prevents rotation or sliding. If longer, the component has unintended axial float. For spring-loaded travel-limiting applications, the shoulder length is deliberately longer than the component stack by the desired travel distance. Always measure the actual component thickness — do not rely on nominal dimensions, as manufactured parts may vary.
What is a low-profile shoulder bolt?
A low-profile shoulder bolt has a reduced head height compared to the standard ISO 7379 socket head. This is used where the assembly envelope limits head protrusion — low-profile heads are thinner but have the same head diameter and socket drive. The trade-off is a smaller bearing face area under the head and a reduced socket depth, which limits the maximum installation torque compared to a standard head. Low-profile shoulder bolts are typically stocked in smaller diameter sizes for electronics and precision equipment applications.