Belts, Chains & Gears
Standard sizes for the common power-transmission parts: V-belt sections, timing belt pitches, ANSI roller chain and gear tooth sizes. Maintenance staff use it to identify a worn belt or chain, and designers use it to pick a standard size before sizing a drive in the Belt/Chain Drive Sizing or Gear Design calculator.
What the page covers
- V-Belt Cross-Section Standards: classical A to E and narrow 3V, 5V and 8V sections, with top width, height and a typical power range per belt [1].
- Timing Belt Pitch Standards: inch trapezoidal (MXL to XH), metric T-series and curvilinear HTD and GT2 pitches [2].
- ANSI Roller Chain Standards: a picker. Choose a chain number and enter the sprocket tooth count, and it shows the pitch, the tabulated tensile strength, the typical use and the sprocket pitch diameter [3], [6].
- Gear Tooth Standards: the preferred modules and the coarse and fine diametral pitches, with the conversion between them [4], [5].
Reading the sizes
A chain number gives the pitch in eighths of an inch from all but its last digit: No. 60 is 6/8 = 0.750″. The sprocket pitch diameter is D = p / sin(180° / N), where p is the chain pitch and N the tooth count. For gears, diametral pitch P is teeth per inch of pitch diameter and module m is millimeters of pitch diameter per tooth, so m = 25.4 / P. A higher P means smaller teeth; a higher m means larger ones. Belt power ranges are per belt and marked “~” because they depend on sheave size and speed.
Limits and common mistakes
- Inch and metric gears don’t mesh. 10 P converts to m = 2.54, which is not the standard 2.5 module.
- Gears mesh only at the same pressure angle. 20° is the current standard; 14.5° survives only for replacement parts.
- T5 and HTD 5M belts share a pitch but not a tooth shape, so they are not interchangeable.
- The chain tensile strength is a breaking load, not a working load. Size the drive with the calculator, and check the maker’s rating.
- The pitch diameter is not the sprocket’s outside diameter, which is larger by roughly half a pitch.
Worked example
A conveyor drive needs a replacement sprocket. The old chain is stamped 50, the sprocket has 19 teeth, and you need the pitch diameter to check the shaft centers.
- Under ANSI Roller Chain Standards, choose ANSI chain number No. 50.
- Set Sprocket teeth (N) to 19.
The picker shows:
Pitch: 0.625 in (15.88 mm)Avg. tensile strength: 4,880 lbf (21,707 N)
Typical use: General industrial
Pitch diameter, 19-tooth sprocket: 3.797 in (96.4 mm)
Check: the pitch matches the stamp, 5/8 = 0.625″. The circle through 19 pitches is about 19 × 0.625 / π = 3.780″. The chordal formula gives slightly more, 3.797″, as it should.
V-Belt Cross-Section Standards
| Section | Top Width | Height | Typical Power Range (HP) |
|---|---|---|---|
| A | 1/2" (13 mm) | 5/16" (8 mm) | ~0.9–10.2 |
| B | 21/32" (17 mm) | 13/32" (11 mm) | ~1.6–16.3 |
| C | 7/8" (22 mm) | 17/32" (14 mm) | ~6.9–31.8 |
| D | 1-1/4" (32 mm) | 3/4" (19 mm) | ~25–100 (indicative) |
| E | 1-1/2" (40 mm) | 29/32" (25 mm) | ~50–200+ (indicative) |
| 3V (narrow) | 3/8" (9.7 mm) | 5/16" (8 mm) | ~1.4–14.2 |
| 5V (narrow) | 5/8" (15.8 mm) | 17/32" (14 mm) | ~8.2–30.8 |
| 8V (narrow) | 1" (25.4 mm) | 7/8" (23 mm) | Similar to 5V-class, higher end |
Timing Belt Pitch Standards
| Designation | Pitch | Family | Typical Use |
|---|---|---|---|
| MXL | 0.080" (2.032 mm) | Inch trapezoidal | Miniature, light instruments |
| XL | 0.200" (5.080 mm) | Inch trapezoidal | Light duty |
| L | 0.375" (9.525 mm) | Inch trapezoidal | Medium load |
| H | 0.500" (12.700 mm) | Inch trapezoidal | Heavy duty |
| XH | 0.875" (22.225 mm) | Inch trapezoidal | Extra heavy duty |
| T2.5 / T5 / T10 | 2.5 / 5 / 10 mm | Metric trapezoidal | Miniature to medium-heavy (not interchangeable with same-number HTD) |
| HTD 3M / 5M / 8M / 14M | 3 / 5 / 8 / 14 mm | Curvilinear (Gates HTD) | Light to heavy duty — 8M is the most common industrial pitch |
| GT2 2mm / 3mm / 5mm | 2 / 3 / 5 mm | Curvilinear (Gates GT2) | Small automation/3D printing to precision positioning |
ANSI Roller Chain Standards
See the Belt/Chain Drive Sizing calculator to size a drive from center distance, ratio, and speed/power.
Gear Tooth Standards
- P
- Diametral pitch — teeth per inch of pitch diameter (higher P = smaller teeth)
- m
- Module — mm of pitch diameter per tooth (higher m = larger teeth)
m = 25.4P
| Standard Modules (mm) | Standard Diametral Pitches (coarse) | Standard Diametral Pitches (fine) |
|---|---|---|
| 0.5, 0.6, 0.8, 1, 1.25, 1.5, 2, 2.5, 3, 4, 5, 6, 8, 10, 12, 16, 20 | 1, 1.25, 1.5, 2, 2.5, 3, 4, 6, 8, 10, 12, 16, 20 | 20, 24, 32, 40, 48, 64, 72, 80, 96, 120 |
See the Gear Design calculator to size a gear mesh, and Gear Train Speed & Torque to solve output speed/torque through a gear train.