HTD-5M 12T-100T Timing Belt Pulleys Pitch 5mm AF-type Drive Pulley Width 21mm

The tooth count determines the pitch diameter and, when paired with a driven pulley, the gear ratio. A smaller drive pulley (fewer teeth) paired with a larger driven pulley (more teeth) reduces speed and multiplies torque. For example, a 20T drive and 40T driven pulley gives a 2:1 reduction. Calculate your required ratio first, then select a tooth count pair that fits within your available center-distance range.

Select the bore diameter that matches your motor or drive shaft. Common stepper motor shaft sizes are 5mm (NEMA 17), 6.35mm (1/4 in, NEMA 23), and 8mm (larger NEMA 23/34). Servo and DC motor shafts often use 8mm, 10mm, or 12mm. If your shaft is metric, match exactly; if imperial (e.g., 1/4 in = 6.35mm), select the 6.35mm bore option.

These pulleys are designed for HTD-5M (5mm pitch, HTD tooth profile) synchronous belts with a 21mm width. They are not compatible with MXL, XL, T5, or GT2 belts, which use different tooth profiles. Verify your belt is labeled HTD-5M or 5M before ordering.

The AF-type hub uses one or two radial set screws that bear directly against the shaft. For light-to-medium torque applications (typical of NEMA 17/23 steppers and small servo motors), set-screw clamping is adequate. For high-torque or reversing-load applications, consider adding a keyway or using a clamp-style hub. Tighten set screws to the manufacturer's recommended torque and use thread-locking compound to prevent loosening under vibration.

Yes. Place the larger tooth-count pulley on the input shaft and the smaller tooth-count pulley on the output shaft to achieve a speed increase with corresponding torque reduction. Ensure your belt tension and bearing loads are appropriate for the higher output speed.

HTD (High Torque Drive) uses a deeper, more rounded tooth profile optimized for high-torque, lower-speed applications. GT2 (Gates Tooth) uses a modified curvilinear profile with tighter tolerances, offering lower backlash and better positional accuracy at higher speeds. These pulleys use the HTD-5M profile and are not interchangeable with GT2 belts or pulleys of the same pitch.

Use the standard belt-length formula: L = 2C + π(D₁+D₂)/2 + (D₂−D₁)²/(4C), where C is center distance and D₁, D₂ are the pitch diameters of the two pulleys. Pitch diameter = (Tooth Count × Pitch) / π. Round up to the nearest available belt length and adjust center distance accordingly. Many online belt-length calculators accept tooth count and center distance directly.