What Is a Synchronous Belt — And How Does It Differ from a V-Belt?
A synchronous belt (also called a timing belt or toothed belt) transmits power through meshing teeth rather than friction. The teeth on the belt engage with corresponding grooves in the pulley, which means the belt and pulley turn in exact ratio with no slip. This is the defining characteristic: synchronous drives maintain a precise speed relationship between shafts.
A V-belt, by contrast, relies on wedging friction in the pulley groove. V-belts are simple, tolerant of misalignment, and can slip under shock load — which is occasionally useful as a form of overload protection. Synchronous belts do not slip, which makes them suitable for positioning drives, servo systems, and any application where shaft timing matters. They also run at lower tension than V-belts and impose smaller bearing loads.
Cogged V-belts (notched belts) are sometimes mistaken for timing belts because their notches look like teeth. They are not. Cogged V-belt notches run in smooth-sided V-pulleys and exist only to improve flexibility and reduce heat build-up. If the pulley has no teeth machined into it, the belt is a V-belt or cogged V-belt — not a synchronous belt. If the pulley has teeth, you have a synchronous drive.
When Synchronous Belts Are the Right Choice
| Application requirement | Synchronous belt advantage |
|---|---|
| Precise shaft timing or indexing | No slip — exact speed ratio maintained |
| No lubrication permissible | Dry-running — no oil or grease required |
| High efficiency required | 98–99% mechanical efficiency vs 93–98% for V-belt |
| Contaminated environment | Less affected by dust and debris than chain drives |
| Low noise requirement | Quieter than chain at equivalent speeds |
| Linear motion or conveying | Open-ended belts available, cut to required length and width |
The Imperial vs Metric Problem
One of the most common sources of confusion with synchronous belts is that two completely separate measurement systems are in use, and both are found in Australian industry. Imperial profiles came first — MXL, XL, L, H, XH, XXH — and were developed in the United States. Metric profiles followed and are now dominant in new equipment design: the T/AT trapezoidal series and the curvilinear HTD and GT3 series all use millimetre dimensions throughout.
The problem is not simply that some belts are measured in inches and others in millimetres. The problem is that a metric belt with a pitch that happens to be numerically close to an imperial equivalent will not fit the same pulley. A T5 belt has a 5mm pitch (0.197"). An XL belt has a 0.200" pitch (5.08mm). Those pitches are close but not equal, and the tooth profiles are completely different. Fitting one to the other's pulley will result in accelerated wear or immediate failure.
The practical rule: always identify the complete specification of the belt and pulley before ordering. Never assume a belt will fit based on pitch alone — confirm the profile family as well.
Belt Profiles: The Complete Reference
Synchronous belt profiles fall into three families: imperial trapezoidal, metric trapezoidal (T and AT series), and curvilinear (HTD and GT3). Within each family, belts are only interchangeable with pulleys of the same profile. Across families, interchangeability is not possible even if the pitch appears similar.
Imperial Trapezoidal Profiles
The original synchronous belt profiles. Tooth angles are typically 40° included angle. Pitch is specified in inches but manufacturers commonly list metric equivalents. All imperial belt part numbers encode the pitch length and width in imperial units.
| Profile | Pitch (inch) | Pitch (mm) | Tooth height (mm) | Typical application |
|---|---|---|---|---|
| MXL | 0.080" | 2.032 | 0.69 | Precision instruments, light office equipment, encoders |
| XL | 0.200" | 5.080 | 1.27 | Light industrial, printers, plotters, small conveyors |
| L | 0.375" | 9.525 | 1.91 | General industrial, packaging machinery, medium duty |
| H | 0.500" | 12.700 | 2.29 | Industrial drives, compressors, pumps, medium–heavy duty |
| XH | 0.875" | 22.225 | 6.35 | Heavy-duty industrial, large compressors, crushers |
| XXH | 1.250" | 31.750 | 9.53 | Very heavy-duty, large industrial equipment |
Imperial belt widths are expressed as a three-digit decimal-inch code in the part number. For example: 025 = 0.25" (6.35mm), 037 = 0.375" (9.525mm), 050 = 0.50" (12.7mm), 075 = 0.75" (19.05mm), 100 = 1.0" (25.4mm), 150 = 1.5" (38.1mm), 200 = 2.0" (50.8mm).
Metric Trapezoidal Profiles: T Series
The T series was developed as a metric alternative to imperial trapezoidal profiles. Tooth angle is 40° (same as imperial) but pitch, dimensions, and widths are all in millimetres. T series belts are widely used in European-designed machinery and are common in Australian industrial equipment manufactured from the 1980s onwards.
| Profile | Pitch (mm) | Tooth height (mm) | Standard widths (mm) | Typical application |
|---|---|---|---|---|
| T2.5 | 2.5 | 0.7 | 6, 10, 16 | Instruments, light positioning, miniature drives |
| T5 | 5.0 | 1.2 | 10, 16, 25, 32 | Light industrial, packaging, small conveyors |
| T10 | 10.0 | 2.5 | 16, 25, 32, 50 | Medium industrial, machine tools, feeders |
| T20 | 20.0 | 5.0 | 32, 50, 100 | Heavy industrial, large conveyors, high-torque drives |
Metric AT Series — The Stronger Trapezoidal Option
The AT series uses the same pitch as the corresponding T series (AT5 = 5mm pitch, AT10 = 10mm pitch) but has a modified tooth geometry that increases the tooth root width and contact area. This gives AT belts significantly higher load capacity at the same pitch compared to standard T belts. AT series is the current preferred choice for new designs where a trapezoidal profile is specified.
| Profile | Pitch (mm) | Standard widths (mm) | Load capacity vs T equivalent |
|---|---|---|---|
| AT5 | 5.0 | 10, 16, 25, 32 | Approximately 20–30% higher than T5 |
| AT10 | 10.0 | 16, 25, 32, 50 | Approximately 20–30% higher than T10 |
| AT20 | 20.0 | 32, 50, 100 | Approximately 20–30% higher than T20 |
T vs AT: Not Interchangeable
This is a common and costly mistake. A T10 belt will not correctly mesh with an AT10 pulley, and vice versa. Despite having the same pitch, the tooth profiles are dimensionally different — the AT tooth is wider at the root with a different flank angle. Running the wrong combination causes rapid tooth wear and premature failure.
If you are replacing a belt in an existing drive, confirm whether the pulley is T or AT before ordering. Most pulleys are marked with the profile code. If the marking is worn, measure the tooth geometry carefully or send a photo for identification before ordering.
Curvilinear Profiles: HTD and GT3
Curvilinear belts have rounded (non-angular) teeth that distribute load across a larger contact area than trapezoidal profiles. This allows higher torque transmission at the same pitch and width. The two dominant curvilinear families in industrial use are HTD and Gates PowerGrip GT3 (and its predecessor GT2).
| Profile | Pitch (mm) | Standard widths (mm) | Key application |
|---|---|---|---|
| HTD 3M | 3.0 | 6, 9, 15 | Light industrial, robotics, light conveyors |
| HTD 5M | 5.0 | 9, 15, 25 | General industrial, pumps, compressors, packaging |
| HTD 8M | 8.0 | 20, 30, 50, 85 | Medium–heavy industrial, machine tools, conveyors |
| HTD 14M | 14.0 | 40, 55, 85, 115, 170 | Heavy-duty industrial, large drives, high-torque applications |
| GT3 (3MGT) | 3.0 | 6, 9, 15 | Precision positioning, robotics, servo drives |
| GT3 (5MGT) | 5.0 | 9, 15, 25 | High-performance industrial drives, servo systems |
| GT3 (8MGT) | 8.0 | 20, 30, 50, 85 | High-torque industrial — upgrade path from HTD 8M |
| GT3 (14MGT) | 14.0 | 40, 55, 85, 115, 170 | Heavy-duty high-torque — upgrade path from HTD 14M |
HTD vs GT3: The Critical Difference
HTD and GT3 belts look similar to the untrained eye — both have rounded teeth with similar pitch options. This visual similarity is exactly why they get confused and mixed up in the field. Getting this wrong will either mean the belt does not seat in the pulley at all, or it runs with incorrect tooth engagement and fails prematurely.
Tooth Geometry
HTD (High Torque Drive) uses a semi-circular tooth profile with a relatively large clearance between tooth and groove. This clearance means HTD drives have measurable backlash — acceptable for power transmission but a limitation for positioning accuracy.
GT3 (Gates PowerGrip GT3) uses a modified curvilinear tooth with a tighter fit in the pulley groove. The optimised tooth geometry reduces backlash significantly and increases the load-bearing contact area. Gates rates GT3 at approximately twice the power capacity of an equivalent HTD drive at the same pitch and width.
Interchangeability — The Rule That Matters
This is where field mistakes happen. The answer depends on the pitch:
| GT3 belt | Same-pitch HTD pulley | Interchangeable? | Notes |
|---|---|---|---|
| 3MGT | HTD 3M | No | Different tooth geometry — will not seat correctly |
| 5MGT | HTD 5M | No | Different tooth geometry — will not seat correctly |
| 8MGT | HTD 8M | Yes | 8MGT belt runs correctly on HTD 8M pulley — upgrade path |
| 14MGT | HTD 14M | Yes | 14MGT belt runs correctly on HTD 14M pulley — upgrade path |
For 8M and 14M pitches, the 8MGT and 14MGT belts can be fitted to existing HTD pulleys as a drop-in upgrade that delivers higher load capacity and lower backlash without changing the pulley. For 3M and 5M pitches, GT3 and HTD are not interchangeable — the correct pulley must be specified alongside the belt.
GT2 vs GT3 — What Changed?
Gates PowerGrip GT2 and GT3 use the same tooth profile. The difference is in the belt construction: GT3 uses an improved body compound and tensile member that gives higher rated load capacity than GT2. GT3 and GT2 belts are dimensionally interchangeable and fit the same pulleys. GT3 is the current production standard; GT2 is the older generation.
When to Specify GT3 Over HTD
- Positioning accuracy required: GT3 lower backlash makes it the right choice for servo drives, CNC axes, and any application where positional error matters
- Higher load in the same envelope: If an HTD drive is marginal on capacity, replacing the belt with GT3 (8M or 14M pitch only) delivers approximately double the rated capacity with no pulley change
- New designs: For any new synchronous drive in the 3M–14M pitch range, GT3 is the current best-practice specification
- HTD is acceptable when: Power transmission only (no positioning requirement), existing HTD pulleys are in good condition and the drive is not overloaded, and cost is a constraint
How to Identify Your Belt
In an ideal situation, the belt markings are visible and legible. Most manufacturers stamp the belt with a code that identifies the pitch length, profile, and width. In practice, belts in service are often installed with markings facing inward, or the markings are faded, oily, or damaged. In these cases, manual measurement is necessary.
Step 1 — Identify the Tooth Profile and Pitch
The tooth profile is the most important dimension to get right. A belt with the wrong profile will either not fit the pulley at all, or will appear to fit but run with incorrect engagement and fail rapidly.
Visual identification:
- Trapezoidal teeth (flat-sided, angular) — imperial (MXL, XL, L, H, XH, XXH) or metric T/AT series
- Rounded, curved teeth — HTD or GT3 curvilinear profile
- T vs AT: visually very similar — AT has a slightly wider tooth root. Measure the tooth at its base and compare to published dimensions, or check the pulley marking.
- HTD vs GT3: also visually similar. Check the pulley for profile markings (usually stamped on the hub or flange). If unsure, do not guess — ask for identification assistance with a photograph and the pitch measurement.
Measuring pitch: Pitch is the centre-to-centre distance between adjacent teeth. Measure carefully from the centre of one tooth to the centre of the next. Use vernier callipers for accuracy. Note: measure using millimetres even for imperial belts, then convert. An XL belt measured in mm gives approximately 5.08mm pitch; a T5 belt gives 5.00mm. Those 0.08mm are meaningful — always check the profile shape alongside the pitch measurement.
Also check the pulleys. Most timing pulleys have the profile and pitch stamped on the face or hub. If the pulley markings are legible, this is the most reliable identification method — it also protects against the previous belt having been the wrong one.
Step 2 — Measure the Belt Length
The length of a synchronous belt is its pitch length — the total circumference measured along the pitch line (not the outer surface or inner surface). For a closed-loop belt, this equals pitch × number of teeth.
Counting method (most reliable for worn belts):
- Mark a reference tooth clearly with a marker or piece of tape
- Count every tooth around the full circumference, returning to the marked tooth
- Multiply total tooth count by the pitch to get pitch length
- Count a second time independently to verify — miscounting by even one tooth gives the wrong belt
Direct measurement: If the belt can be removed and laid flat, measure the pitch line length directly. Use a flexible tape along the tooth pitch line, not the outer surface.
Imperial belt length coding: Imperial belt part numbers express pitch length in decimal inches. For example, a 420H100 belt has a pitch length of 42.0 inches (420 ÷ 10). An XL part number uses 1/100 of an inch: 270XL037 = 2.70 inch pitch length. The metric equivalent is typically listed in manufacturer tables.
Step 3 — Measure the Width
Belt width is straightforward: measure across the full belt face with callipers or a ruler. Allow for wear — a belt in service may be slightly narrower than its nominal width due to edge wear. Compare against the standard width table for the profile to confirm the correct nominal width to order.
Note on worn belts: A belt that has been running in a misaligned drive will show asymmetric edge wear. In this case, use the pulley groove width to determine the correct belt width rather than the worn belt edge.
How to Read a Timing Belt Part Number
Part number formats vary by profile family. The key principle is the same: pitch length, profile identifier, width code — in that order.
| Format | Example | Decoded |
|---|---|---|
| Imperial (H, XL, L…) | 420H100 | Pitch length 42.0" · H profile · 1.00" wide |
| Imperial (XL) | 270XL037 | Pitch length 2.70" · XL profile · 0.375" wide |
| Metric T/AT | 500T10/25 | Pitch length 500mm · T10 profile · 25mm wide |
| Metric T/AT | 750AT10-32 | Pitch length 750mm · AT10 profile · 32mm wide |
| HTD | 600-5M-15 | Pitch length 600mm · HTD 5M profile · 15mm wide |
| GT3 (Gates) | 960-8MGT-30 | Pitch length 960mm · GT3 8M pitch · 30mm wide |
Note that different manufacturers may use slightly different separators or ordering conventions. Gates, Bando, and Continental all follow broadly similar conventions for each profile family, but always cross-reference the full specification rather than assuming a part number from one manufacturer is a direct equivalent of another's.
Belt Width: Standard Sizes and Cut-to-Width Options
Synchronous belts are manufactured in standard widths for each profile, as listed in the profile tables above. For most power transmission drives, a standard width belt is the right and most economical choice.
Open-Ended Belts — Cut to Length and Width
For linear motion applications, conveyor positioning drives, and custom automation equipment, synchronous belts are available in open-ended (cut) form. Open-ended belts are supplied as a continuous roll or long linear length and can be cut to the precise length required for the application. This is the standard approach for:
- Linear drives — automated doors, material handling gantries, X-Y positioning tables
- CNC machine tool axes where a standard closed-loop length is not available
- Long conveyor runs where a closed-loop belt of the required length is not a standard stock item
- Robotics and pick-and-place systems with non-standard travel lengths
Open-ended belts can also be cut to a non-standard width. This is useful when the required width falls between standard sizes, or when an application calls for a custom width to match an existing pulley groove. The belt is cut from a wider roll using a precision slitting process. This service is available on enquiry — contact us with the required profile, pitch length, and width.
Standard profiles available in open-ended form: XL, L, H (imperial), T5, T10, T20, AT5, AT10, AT20, HTD 5M, HTD 8M, and GT3 profiles. Availability depends on pitch and width — contact us to confirm stock for your specification.
Belt Materials
The base material of the belt body and the tensile cord construction determine how the belt performs in service. Most industrial synchronous belts use one of three body compounds, paired with a fibre-reinforced tensile cord.
Neoprene (CR) — Standard Construction
Neoprene (chloroprene rubber) is the standard body compound for industrial synchronous belts. It provides good resistance to oil and ozone, adequate temperature range (−30°C to +100°C continuous), and excellent flex fatigue life. The tooth facing is typically a nylon fabric that reduces wear and friction at the tooth surface. Tensile cord is fibreglass or aramid (Kevlar).
Neoprene belts are the correct choice for the majority of industrial drives and are the standard stocked product. If no special environmental conditions apply, specify neoprene.
Polyurethane (PU) — Chemical Resistance and Longevity
Polyurethane belts offer several advantages over neoprene in specific applications:
- Chemical resistance: Better resistance to fuels, hydraulic oils, greases, and many solvents that cause neoprene to swell or degrade
- Flex fatigue life: PU belts typically outlast neoprene in applications with small pulley diameters or high cycle rates
- Cleanliness: Available in white or natural colour with steel tensile cord — suitable for food and pharmaceutical applications where dark particles from neoprene are not acceptable
- Open-ended stock: PU is the standard material for open-ended belt rolls used in linear motion applications
PU belts are slightly less flexible than neoprene and have a lower continuous temperature rating in some constructions. They are also more expensive. Specify PU when chemical exposure, hygiene requirements, or very long service life in high-flex applications justifies the cost.
FRAS — Fire-Resistant Anti-Static
FRAS (Fire-Resistant Anti-Static) belts are compounded to resist ignition and to dissipate static electricity rather than accumulate it. This is the specification required for underground mining, above-ground mining with explosion risk, grain handling, petrochemical plants, and other environments where ignition of flammable dust, gas, or vapour by a belt-generated spark or fire is a foreseeable hazard.
FRAS requirements in Australia are typically assessed against ISO 1813 (anti-static, <300 MΩ surface resistance) and fire resistance testing relevant to the specific industry standard (e.g., AS 1333 for conveyor belts, mining-specific standards for underground applications).
AIMS stocks FRAS V-belts (PIX FRAS-XS range) in A, B, and C sections for standard power transmission drives in hazardous areas. FRAS synchronous/timing belts are available on special order. If your application requires a FRAS-rated synchronous belt, contact us with the belt specification and application details and we will source the correct product.
Selection Guide
Selecting the right synchronous belt for a new design or a re-design involves more than matching the pitch and width of the existing belt. The following steps apply to any new synchronous drive selection.
1. Determine the Design Power
Design power accounts for the actual load plus any service factors for shock, starting conditions, and duty cycle:
Design power (kW) = Transmitted power (kW) × Service factor
Common service factors:
| Load type | Service factor |
|---|---|
| Smooth, uniform load (fans, centrifugal pumps, light conveyors) | 1.0–1.2 |
| Moderate shock (reciprocating compressors, general industrial machinery) | 1.3–1.5 |
| Heavy shock (crushers, hammer mills, reversing drives) | 1.6–2.0 |
| Positioning drives, servo systems (add accuracy factor) | Consult manufacturer data |
2. Select the Pitch
Pitch selection is primarily driven by speed (rpm of the faster shaft) and power. As a general guide for the curvilinear profiles:
| Pitch | Approximate speed range (rpm, faster shaft) | Power range |
|---|---|---|
| HTD 3M / GT3 3MGT | Up to 8,000 rpm | Up to ~2 kW |
| HTD 5M / GT3 5MGT | 500–6,000 rpm | 0.5–15 kW |
| HTD 8M / GT3 8MGT | 200–4,500 rpm | 2–75 kW |
| HTD 14M / GT3 14MGT | 100–2,500 rpm | 15–300+ kW |
These are indicative ranges only. Always refer to the belt manufacturer's published design tables or use their online design tool for final specification. Gates provides detailed design data for all PowerGrip profiles.
3. Determine Width
Once pitch is selected, width is determined from the manufacturer's power rating tables for the selected pitch at your design speed. Multiple standard widths are available for each pitch — a wider belt carries more load. Select the narrowest standard width that meets or exceeds the design power requirement.
4. Check Minimum Pulley Diameter
Each belt profile has a minimum recommended pulley tooth count (and therefore minimum pitch diameter). Running below the minimum tooth count causes excessive bending stress at the pulley and reduces belt life significantly. Confirm both driver and driven pulleys meet the minimum tooth count for the selected profile.
Installation and Tensioning
Unlike V-belts, synchronous belts do not rely on high tension for power transmission. The teeth carry the load. However, correct tension is still critical: too little tension causes the belt to skip teeth (ratcheting) under load; too much tension overloads the shaft bearings and shortens both belt and bearing life.
Installation Procedure
- Power down and lock out: Always isolate and lock out the drive before working on belt systems. Apply a LOTO device before removing any guards.
- Reduce centre distance: Move the motor or tensioner to allow the belt to be slipped over the pulleys without forcing it over the teeth. Never lever a synchronous belt onto a pulley — this damages the tensile cord.
- Check pulley alignment: Shaft centrelines must be parallel and pulley faces must be co-planar. Misalignment causes edge wear and reduces belt life. Use a straight edge across both pulley faces to check alignment before tensioning.
- Set initial tension: Increase centre distance until the belt is approximately at running tension. For new installations, refer to the manufacturer's span deflection tables or use a sonic tension meter for accurate tensioning.
- Check tension after first run: New belts stretch slightly during initial operation. Re-check and adjust tension after the first 4–8 hours of operation.
Span Deflection Method
The simplest field tensioning method is span deflection. Apply a known force at the midpoint of the free span and measure the deflection. The correct deflection for a given span, profile, and speed can be calculated from manufacturer data. Gates publish span deflection tables for all PowerGrip profiles in their application manual.
Sonic Tension Meters
A sonic tension meter (such as the Gates Sonic Tension Meter) measures belt tension by detecting the natural frequency of the belt span, similar to tuning a guitar string. This is the most accurate field method and eliminates guesswork on new installations and maintenance checks. The meter app calculates the correct target frequency for the profile, span length, and belt mass per unit length.
Failure Modes and Troubleshooting
| Failure mode | Appearance | Most likely causes |
|---|---|---|
| Tooth ratcheting (skipping) | Belt jumps teeth under load; teeth shear off | Under-tension; overload; shock load; wrong belt/pulley combination; insufficient tooth wrap on small pulley |
| Tooth shear | Teeth torn cleanly or in chunks from belt body | Severe overload; jam or sudden reversal; foreign object in drive; grossly under-tensioned |
| Edge wear / cracking at edges | Belt edges fraying, cracking, or worn asymmetrically | Misalignment (shaft or pulley); flange contact; belt tracking out of groove |
| Transverse (body) cracks | Cracks across the belt back, perpendicular to running direction | Excessive bending (pulley too small); age / ozone degradation; oil contamination; temperature extremes |
| Tensile failure | Belt snaps across full width | Severe overload or shock; over-tensioning; damaged tensile cord (from levering belt on pulley); foreign object |
| Accelerated tooth wear (no failure yet) | Teeth rounded off, shorter than original profile | Wrong profile on pulley; over-tension; abrasive contamination; excessive speed or load |
| Belt noise (whine or chatter) | High-pitched or rhythmic noise at speed | Under-tension (most common); misalignment; resonance at operating frequency; worn pulleys |
| Oil contamination | Belt swelling, tackiness, rapid softening of tooth surface | Oil or grease from adjacent bearing; specify PU belt or improve sealing in contaminated environments |
General principle: When a belt fails repeatedly in a short time after replacement, the belt is usually not the root cause. Look at the drive design: correct profile, adequate belt rating for the design power, correct tension, proper alignment, and minimum pulley diameters. Replacing a belt without addressing the root cause produces the same failure again.
Frequently Asked Questions
What is the difference between a synchronous belt and a V-belt?
A synchronous belt has teeth that mesh with a toothed pulley, transmitting power without slip at an exact speed ratio. A V-belt relies on friction wedging in a smooth V-groove and can slip under overload. Synchronous belts are the correct choice for any application requiring precise shaft timing, positioning accuracy, or high efficiency. V-belts are simpler to install and more tolerant of misalignment, making them suitable for general power transmission where exact synchronisation is not required.
Are HTD and GT3 belts interchangeable?
It depends on the pitch. For 8M and 14M pitches, GT3 belts (8MGT, 14MGT) can be fitted to existing HTD 8M and HTD 14M pulleys — this is a supported upgrade path that delivers approximately double the load capacity with no pulley change. For 3M and 5M pitches, GT3 (3MGT, 5MGT) and HTD belts have different tooth geometry and are not interchangeable. A 5MGT belt will not correctly mesh on an HTD 5M pulley. Always confirm the pulley profile before ordering a replacement belt.
Are T and AT timing belts interchangeable?
No. T and AT belts have the same pitch (T10 and AT10 are both 10mm pitch) but different tooth profiles. The AT tooth is wider at the root with a different flank geometry. A T10 belt fitted to an AT10 pulley — or vice versa — will not mesh correctly and will wear rapidly. Check the pulley or existing belt marking to confirm whether the drive uses T or AT before ordering a replacement.
What is an open-ended timing belt and when should I use one?
An open-ended belt is a synchronous belt supplied in a straight length rather than a closed loop. It is cut to the required length from a roll or long stock length and is the standard approach for linear motion drives, conveyor positioning systems, and CNC machine tool axes where a standard closed-loop belt length is not available. Open-ended belts can also be slit to non-standard widths on request. Contact us with the profile, pitch, and required dimensions.
How do I identify my timing belt profile without the markings?
First, determine whether the teeth are trapezoidal (flat-sided, angular) or curvilinear (rounded). Trapezoidal teeth indicate imperial (MXL, XL, L, H) or metric T/AT series. Rounded teeth indicate HTD or GT3. Next, measure the pitch (centre-to-centre between adjacent teeth) accurately in millimetres. Compare the pitch and tooth shape against the profile tables. Also check the pulley — most timing pulleys are marked with the profile code on the hub or face, which is often more reliable than measuring a worn belt. If you are uncertain, send photographs and measurements to us for identification assistance.
What does the part number on a timing belt mean?
The part number encodes pitch length, profile, and width. For imperial belts: 420H100 = 42.0" pitch length, H profile, 1.00" wide. For metric T/AT belts: 500T10/25 = 500mm pitch length, T10 profile, 25mm wide. For HTD: 600-5M-15 = 600mm pitch length, HTD 5M profile, 15mm wide. For Gates GT3: 960-8MGT-30 = 960mm pitch length, GT3 8M pitch, 30mm wide. The format varies slightly between manufacturers but always follows the same sequence: length, profile, width.
What is the difference between imperial and metric timing belts?
Imperial belts (MXL, XL, L, H, XH, XXH) were developed in the United States and use inch-based pitch and width dimensions. Metric belts (T/AT series, HTD, GT3) use millimetre dimensions throughout. Beyond the measurement system, the tooth profiles are completely different between families. A metric belt with a pitch close to an imperial equivalent (e.g., T5 at 5.0mm vs XL at 5.08mm) is not interchangeable with it — the tooth shape is different. Always identify both the pitch and the profile family before ordering.
When should I use a polyurethane belt instead of neoprene?
Specify polyurethane (PU) when: the drive is exposed to oil, fuel, or chemical contamination that would degrade neoprene; the application is food or pharmaceutical and belt particles must not contaminate the product (PU is available in white); the drive involves small pulleys with high cycle rates where PU’s flex fatigue life outperforms neoprene; or the belt is an open-ended linear drive (PU is the standard material for open-ended rolls). For standard industrial power transmission drives without these special requirements, neoprene is the correct and more economical choice.
What belt do I need for a mining or hazardous environment?
Drives in underground mines, above-ground sites with explosion risk, grain handling facilities, petrochemical plants, and other hazardous-atmosphere environments require FRAS (Fire-Resistant Anti-Static) rated belts. FRAS belts are compounded to resist ignition and dissipate static charge, addressing the two main ignition risks from belt drives. AIMS stocks FRAS V-belts (PIX FRAS-XS range in A, B, and C sections). FRAS synchronous timing belts are available on special order — contact us with your specification and application details.
How do I know if my synchronous belt is tensioned correctly?
The most accurate method is a sonic tension meter, which measures belt tension from the natural vibration frequency of the free span. The Gates Sonic Tension Meter app calculates the correct target frequency for any belt specification. In the field, span deflection is the practical alternative: apply a measured force at the midspan centre and check that the resulting deflection matches the value from the manufacturer’s tension table. Under-tension produces audible noise (whine or chatter) at speed; over-tension causes accelerated bearing wear on the shaft nearest the belt. Correct tension is quiet running with no tooth jumping under peak load.
What causes timing belt tooth ratcheting?
Ratcheting (tooth skipping) occurs when the teeth jump out of mesh under load. The primary causes are: insufficient belt tension; overloading the drive beyond its rated capacity; shock loads or sudden reversals; incorrect belt profile on the pulley (poor tooth engagement); insufficient tooth wrap on the small pulley (too few teeth in mesh); and pulley damage or worn tooth grooves reducing mesh depth. Ratcheting is a destructive event — even a single skip episode typically damages tooth surfaces. When ratcheting occurs, address the root cause before fitting a new belt.
Can a synchronous belt run in both directions?
Yes. Synchronous belts have no directionality in normal operation — they can be driven in either direction or reversed. For serpentine drives where the belt must wrap around a back-tension idler on the non-toothed side, double-sided synchronous belts are available. A double-sided belt has teeth on both the inner and outer faces, allowing power take-off from both sides of the belt simultaneously. Specify double-sided when the drive geometry requires it.
How do I order a timing belt if I only have the old belt and it is damaged?
A damaged or partially destroyed belt can still yield the information needed for replacement. Identify the tooth profile from the shape (trapezoidal vs curvilinear) and measure the pitch from any undamaged section. Count teeth on the largest intact section and extrapolate to the full circumference, or measure the remaining pitch length and add the missing section if it can be estimated from pulley dimensions. Measure the width. Check the pulleys for markings. If the belt is too damaged for reliable measurement, send photographs of the belt, the pulleys, and any visible markings to us and we will assist with identification.
View our full range of synchronous timing belts: Industrial Timing Belts — Bearings & Power Transmission