S3M - Zahnrad - Pulley/ Zahnriemenrad Riemenscheibe/ 20- 120Zähne/Breite 15/20mm

The tooth count determines the pitch diameter and, combined with your motor pulley, sets the drive ratio. A higher tooth count gives a larger pitch diameter and lower belt tension for the same torque. Match the tooth count to your required linear speed or gear ratio — for most desktop CNC and 3D printer axes, 20Z–40Z is typical for the motor pulley, while larger counts suit idler or driven-shaft pulleys.

A plain bore is a smooth cylindrical hole secured to the shaft with one or more set screws. A keyway bore (e.g., K4 = 4 mm keyway) includes a machined slot that accepts a matching key on the shaft, providing a positive mechanical lock that resists rotational slipping under high torque. Choose keyway variants for high-load or high-cycle applications; plain bore is sufficient for most light-duty DIY builds.

Yes. These pulleys are machined to the S3M synchronous belt standard (3 mm pitch). They are compatible with any S3M open-ended or closed-loop timing belt of matching width (15 mm or 20 mm). Confirm your belt width before selecting a variant.

Measure your motor or drive shaft diameter with a caliper. Select the bore size that matches — for example, a NEMA 17 stepper motor typically has a 5 mm shaft, so choose bore 5. For a 1/4-inch (6.35 mm) shaft, select bore 6.35. If you need a keyway, choose the corresponding K-suffix variant (e.g., 10K3 = 10 mm bore with 3 mm keyway).

The pulleys are machined from aluminum alloy, which offers a good strength-to-weight ratio and natural oxidation resistance in typical indoor environments. For outdoor or high-humidity applications, consider applying a light coating of machine oil to the bore and tooth surfaces to prevent surface oxidation over time.

Technically the belt will run on the pulley, but it is not recommended. Mismatched belt and pulley widths can cause uneven tooth wear, belt tracking issues, and reduced load capacity. Always match the belt width to the pulley belt-contact width for reliable, long-term operation.

The 120-tooth variant has a significantly larger pitch diameter and is typically used as a driven pulley in high-reduction belt drives, as a large idler, or in applications requiring a very low output speed from a high-speed motor. It is available in 15 mm width with bore sizes from 15 mm to 25 mm, including keyway options.