Inch: tenths and hundredths
390L100 is 39.0 in long, L pitch (3/8 in), 1.00 in wide: 104 teeth. Width codes are hundredths of an inch: 025 is 1/4 in, 037 is 3/8 in, 100 is 1 in.
Reference tool — not a selection
Read a timing belt before it goes in an RFQ.
Timing belt
Pitch, length, teeth.
Type the designation. Put an offered replacement in the second field, and the reader checks the pitch and profile, the teeth and the width. The belt, the tooth profile and the RFQ line update with every change.
Examples:
Replacement check
On the designations alone: the maker’s catalogue and the pulleys decide.
All 130 engineering tools
A timing (synchronous, toothed) belt is named by its pitch, its pitch length and its width. Inch belts write the length in tenths of an inch, the pitch code and the width in hundredths of an inch, as in 390L100; metric belts give the length, the pitch in millimetres with the profile letters and the width in millimetres, as in 1200-8M-30. Type the designation, and the reader gives the pitch, the length, the number of teeth and the width, draws the belt running on two pulleys and writes the RFQ line.
Several tooth profiles share one metric pitch, and close pitches do not mesh: an 8M belt does not run on an L pulley, nor a T10 on an H pulley. Quote the profile letters exactly as printed.
How a designation is read
Length, pitch, width.
Metric: millimetres
1200-8M-30 is 1200 mm long, 8 mm pitch, 30 mm wide: 150 teeth. T10-1210 is a T10 belt 1210 mm long; its width is given separately.
Teeth are a whole number
The pitch length divided by the pitch is the tooth count, and it must come out whole. If it does not, the length or the pitch is misread.
| Code | Pitch, in | Pitch, mm | Profile |
|---|---|---|---|
| MXL | 0.080 in | 2.032 | inch trapezoidal |
| XL | 1/5 in | 5.08 | inch trapezoidal |
| L | 3/8 in | 9.525 | inch trapezoidal |
| H | 1/2 in | 12.7 | inch trapezoidal |
| XH | 7/8 in | 22.225 | inch trapezoidal |
| XXH | 1 1/4 in | 31.75 | inch trapezoidal |
| T2.5, T5, T10 | — | 2.5, 5, 10 | metric trapezoidal |
| AT5, AT10 | — | 5, 10 | metric trapezoidal, stronger tooth |
| 3M, 5M, 8M | — | 3, 5, 8 | metric curvilinear (HTD) |
MXL numbers are read two ways: Texas Belting reads 112MXL025 as 11.2 in long (140 teeth), and B&B says most makers number MXL belts by tooth count. The reader shows both readings.
Sources
Inch pitches, codes and examples: Texas Belting, "Trapezoidal Timing Belts", and B&B Manufacturing (Solve Industrial Motion Group), "How to identify a timing belt"; the pitch table of Gates. Metric designations and the 640-8MX-12 example: B&B. Pitches that look close but do not mesh (8M on L, T10 on H): Texas Belting.
Before you send the belt
Questions about timing belts in an RFQ
What does 390L100 mean?
A 39.0 in pitch length, L pitch (3/8 in, 9.525 mm), 1.00 in wide. 39.0 divided by 0.375 gives 104 teeth.
What does 1200-8M-30 mean?
A metric belt of 1200 mm pitch length with an 8 mm curvilinear (HTD) tooth, 30 mm wide: 150 teeth.
Is a T10 belt the same as an H belt?
No. T10 has a 10 mm pitch and H 12.7 mm, and an 8M belt does not run on an L pulley either, although the pitches look close. Match the pitch and the profile letters exactly.
What should the request include?
The whole designation from the belt, the maker, the width, the tooth count if the print is worn, the material (neoprene or polyurethane) and the machine. A photograph of the belt back and of the pulley helps.
Belt read?
Send the line with the photographs.
A decoded designation is a cross-check, not proof. Attach photographs of the belt and the pulley, and Vessel Core checks them before an offer goes back.
Buyer tools
