RESOURCE CENTER
Timing Belts 101
A working introduction to how timing belts are built, the tooth profiles that matter, and how to read a belt designation.
How a Timing Belt Is Built
A timing belt is a reinforced rubber or polyurethane band with teeth on the inside face. Three elements do the work:
- Tension members — cords running the full belt length, embedded near the pitch line. They carry the working load and control stretch.
- Tooth profile — the shape of the teeth, which engages matching grooves in the pulley. It determines torque capacity and noise.
- Belt body — the rubber or polyurethane matrix that bonds the tension members and teeth into one part and resists wear, oil, and temperature.
The pitch line (where the tension members sit) is the neutral axis — it neither stretches nor compresses as the belt bends around pulleys. This is why belt length is measured at the pitch line, not at the tooth tip.
Tooth Profile Types
Curvilinear: HTD and GT2
HTD (High Torque Drive) and GT2 (Gates Tooth) use rounded teeth that engage progressively with the pulley groove. The larger contact area spreads load, which allows higher torque at the same width and quieter operation.
| Profile | Pitch | Use |
|---|---|---|
| GT2 | 2 mm (3GT: 3 mm) | 3D printers, CNC, light motion |
| HTD 5M | 5 mm | Linear actuators, small conveyors |
| HTD 8M | 8 mm | General power transmission, packaging |
| HTD 14M | 14 mm | Heavy industrial drives |
Trapezoidal: T, AT, and Imperial (MXL, XL, L, H)
Trapezoidal teeth are straight-sided, engaging the pulley with a wedging action. They are the traditional metric (T5, T10, AT5, AT10) and imperial (MXL, XL, L, H, XH) profiles. They remain common in legacy equipment — replacement means matching the existing profile.
Tension Member Materials
| Tension Member | Stiffness | Strength | Best For |
|---|---|---|---|
| Fiberglass | Low stretch | Standard | General drives, economical |
| Aramid (Kevlar-type) | Moderate | High | Shock loads, high speed |
| Steel | Maximum | Highest | Precision linear drives |
How to Read a Belt Designation
A designation like HTD 8M-30-1440 breaks down as: profile (HTD 8M = 8 mm pitch curvilinear), width (30 mm), and length (1440 mm = 180 teeth × 8 mm). A GT2 designation like GT2-6-1000 means 2 mm pitch, 6 mm wide, 1000 mm long. For endless belts, length is always a whole number of teeth × pitch.
Open-Ended vs Endless
Open-ended belts are continuous rolls, cut to length and anchored at both ends — standard for linear drives. Endless belts are molded or welded loops — standard for power transmission and conveyors. Double-sided belts have teeth on both faces for serpentine paths.
Not Sure Which Belt You Need?
Send us the belt you are working with — pitch, width, length, or a photo — and we will identify it and confirm the right replacement.