How do I read a timing belt part number like 800-8M-30?

Question

Accepted Answer

Direct answer: 800-8M-30 means 800 mm pitch length, 8M tooth profile on an 8 mm pitch, and 30 mm width. Metric codes read length first, then profile, then width; imperial codes put the profile letter after the length in inches and the width in hundredths of an inch.

The same data in a different order: 8M-2320-35 is an 8M belt, 2320 mm pitch length, 35 mm wide.

Decoding metric and imperial codes

Code	Pitch length	Profile	Width
800-8M-30	800 mm	8M, 8 mm pitch	30 mm
2320-14M-40	2320 mm	14M, 14 mm pitch	40 mm
320L075	32.0 in (812.8 mm)	L, 3/8 in pitch	0.75 in (19.05 mm)
120XL025	12.0 in (304.8 mm)	XL, 1/5 in pitch	0.25 in (6.35 mm)
450H100	45.0 in (1143.0 mm)	H, 1/2 in pitch	1.00 in (25.4 mm)

Common profiles and their pitches

Profile	Pitch	Typical use
MXL	2.032 mm	Small instruments and light drives
XL	5.08 mm	Light duty machinery
L	9.525 mm	General light industrial drives
H	12.7 mm	Medium load drives
3M / 5M / 8M / 14M	3 / 5 / 8 / 14 mm	Metric drives from light to heavy duty
AT, STD, RPP	Metric, modified tooth form	Higher load, quieter running, positioning drives

Why the length on the belt is not what you measure

Timing belt length is the pitch length, measured along the cord line inside the belt. A tape run around the outside gives a different number, and a worn or stretched belt reads longer than its code. If the marking has gone, measure the width and count the teeth: pitch length equals the number of teeth multiplied by the pitch. A 1624 mm 8M belt therefore has 203 teeth.

8M timing belt marked 8M-1624-30 — 8M-1624-30: 1624 mm pitch length, 203 teeth, 30 mm wide.

Profile letters are not freely interchangeable. An 8M pulley and an S8M belt share the 8 mm pitch but not the tooth form, and imperial L and metric 8M belts are not substitutes. Send the full code plus a photo of the pulley teeth when you order.

S8M runs on the same 8 mm pitch as 8M but with a different tooth form, so always order by the full code (S8M-984-50).

How to specify a belt when the code is worn off

Measure the belt width across the flat back, in millimetres.
Count the teeth over the whole belt, then multiply by the pitch to get the pitch length.
Identify the profile from the pulley, not from the old belt, because a worn belt can look like a different tooth form.
Send one photo of the belt marking and one of the pulley tooth profile and we will confirm the match.

Send the code and we will match it

Email the belt code, a photo of the belt and one of the pulley tooth profile, plus the quantity, to sales@goodlybelts.com. We will confirm the profile and length and quote the equivalent GOODLY belt.

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