The Different Timing Belt Pitches

1. What is “pitch” in a synchronous (timing) belt drive?

In a synchronous belt drive (also called a timing belt drive), the pitch (or tooth pitch) is defined as the distance between the centers of two adjacent teeth along the pitch line (or the belt’s pitch circle).

This matters because the belt must mesh with a matching toothed pulley or sprocket having the same tooth spacing. If the pitch doesn’t match, you’ll have poor engagement, noise, slippage or premature wear.

In design terms:

• The tooth pitch (in mm or inch) defines which belt profile is used.

• It influences minimum pulley diameter, speed limits, load-capacity, and belt width.

2. Imperial step-codes: MXL, XL, L, H, XH, XXH

Historically many timing belt drives (especially in the U.S./UK) used imperial-dimension profiles, standardized under e.g. ISO 5296‑1. Below is a summary of common imperial pitch codes:

Comments and design notes:

• These codes indicate the pitch (distance between tooth centres) rather than the belt width.

• As pitch increases (toward H, XH, XXH), the belts can handle larger loads, larger pulley diameters, more torque, but with lower resolution (i.e., fewer teeth per given circumference) and often larger minimum pulley diameters.

• Using a profile mismatched leads to meshing problems, increased wear, noise, etc.

• The standard ISO document lists these as “Belts — Part 1: Pitch codes MXL, XL, L, H, XH and XXH — Metric and inch dimensions.”

3. Metric pitch systems: 1.5M, 2M, 3M, 5M, 8M, 14M (and others)

In the metric world (especially Europe / Asia), timing belts are often specified by the tooth pitch in millimetres, using codes such as 1.5M, 2M, 3M, 5M, 8M, 14M, 20M etc. For example:

• The term “14M” refers to a belt with ~14 mm pitch.

• Designers can order belts open-ended of e.g. 1.5 m, 3 m, 7.5 m, etc length for linear drives.

Here is a typical list of metric pitch profiles with approximate values and comments:

Notes:

• These metric codes are often used for “open ended” belts (for instance linear drives) and for synchronous drives where a specific mm-pitch is required. Example product “2450-14M-115” shows a 14 mm pitch belt.

• Designers must ensure the pulley/groove system is matched to the pitch.

• Using a metric pitch variant allows more teeth per given length than a large-pitch belt — giving finer resolution, smoother motion, lower minimum diameter etc, at the cost of smaller load capacity generally.

• The metric systems often allow “endless” belts of long lengths (several metres) for linear or wrap-around drives.

4. Conversion and selecting which pitch to use

Conversion & matching:

• In the imperial series: 0.080 inches = 2.032 mm (MXL) etc. See the table above.

• Ensure belt pitch + pulley groove pitch match exactly (either imperial code to imperial code, or metric to metric).

• If a machine design originates in one standard and needs sourcing in another, you may need to cross-reference or choose equivalent profile.

Choosing the pitch:

Consider these factors:

• Torque / load: Larger pitch (e.g., H, XH, XXH or 14M, 20M) handle higher loads.

• Speed & resolution: Smaller pitch (e.g., MXL, XL or 1.5M, 3M, 5M) give more teeth per unit length → smoother motion, better accuracy, lower minimum pulley diameter.

• Centre distance: For long centre distances or wrap around configurations you might use small pitch but then ensure belt length, tensioning, idlers are suitable.

• Pulley diameter minimum: Smaller pitch allows smaller pulley diameters; larger pitch typically requires a larger minimum diameter.

• Economics / availability: Some profiles are more common (and cheaper) in certain regions.

• Matching to existing machine standard: If replacing parts on equipment built to imperial codes, stick to those to avoid needing new pulleys.

Example Guidelines:

• A lightweight indexing drive on a small machine might use XL (0.200 in / ~5.08 mm) or 5M (~5 mm) profile.

• A medium industrial machine might use L (0.375 in / ~9.525 mm) or 8M (~8 mm).

• A heavy industrial drive, long centre-distance or high torque: H (0.500 in / ~12.7 mm) or 14M (~14 mm) or above.

• For ultra‐heavy / large drives: XXH (1.250 in / ~31.75 mm) or metric 20M etc.

5. Summary tables for quick reference

Imperial (inch-based) series:

• MXL → 0.080 in (≈2.032 mm)

• XL → 0.200 in (≈5.080 mm)

• L → 0.375 in (≈9.525 mm)

• H → 0.500 in (≈12.700 mm)

• XH → 0.875 in (≈22.225 mm)

• XXH → 1.250 in (≈31.750 mm)

Metric series (common pitches):

• 1.5M → ~1.5 mm

• 2M → ~2.0 mm

• 3M → ~3.0 mm

• 5M → ~5.0 mm

• 8M → ~8.0 mm

• 14M → ~14.0 mm

• (20M → ~20.0 mm)

6. Practical tips & cautions

• Always verify both belt & pulley pitch codes before purchase. Mismatched pitch = poor fit + reduced life.

• For retrofit/interchange: If your machine uses imperial profile and you can’t source belt easily, consider whether pulleys can be changed to metric or vice-versa — but factor cost.

• Remember minimum pulley diameter: smaller pitch allows tighter pulleys, but larger pitch may demand large pulleys or idler support.

• Pulley manufacturing precision matters: tooth form, backlash, surface finish influence performance (especially for fine pitch).

• Tensioning & maintenance: timing belts don’t rely on slip but on tooth engagement — ensure proper tension and alignment.

• Environmental factors: Some belts (especially metric ones) are available in extended lengths, special materials, anti-static versions. (See 14M & 20M series for high performance)

7. Conclusion

The choice of timing-belt pitch fundamentally impacts the design and performance of a synchronous drive. Whether using the traditional imperial profiles (MXL → XXH) or the metric-pitch series (1.5M → 14M → …), the key is to match the belt pitch with the pulley profile, understand the trade-offs (load, speed, resolution, economy) and select the correct type for your application. With correct selection and maintenance, the drive will perform reliably and efficiently.