S3M Timing Belt Pulley Synchronous Wheel 30 - 40 Teeth Bore 5 - 25mm Aluminum

The number of teeth determines the pulley's pitch diameter and, combined with your belt length and the driven pulley's tooth count, sets your drive ratio. For a 1:1 ratio use identical tooth counts on both pulleys. For speed reduction or torque multiplication, select a larger tooth count on the driven side. Common desktop CNC and 3D printer designs use 20–40 tooth pulleys; 30–40 teeth offer a slightly larger pitch diameter, which can reduce belt wrap angle issues on short center distances.

BF-Type pulleys have flanges on both sides of the tooth profile. The flanges act as guides that keep the belt centered on the pulley during operation, which is important on horizontal or angled axes where gravity or side loads could cause the belt to walk off. K-Type pulleys have no flanges, making them suitable for applications where the belt must be able to shift laterally, or where space constraints prevent the use of flanged pulleys. In most paired-pulley systems, at least one pulley should be flanged.

Measure your motor or drive shaft diameter with calipers before ordering. Common stepper motor shaft diameters are 5 mm, 6 mm, 6.35 mm (1/4 in), and 8 mm. Servo motors often use 10–25 mm shafts. Select the bore that matches your shaft exactly — a bore that is too large will cause runout and belt skip even when the set screw is tightened. If your shaft has a flat (D-cut), position the set screw over the flat for the most secure retention.

Yes, provided the belt width matches the slot width of the pulley you select. The 11 mm slot width variant is designed for S3M belts up to 10 mm wide; the 16 mm slot width variant accommodates belts up to 15 mm wide. Always verify that the belt pitch is S3M (3 mm) — do not mix with GT2, HTD, or other pitch profiles, as the tooth geometry is not interchangeable and will cause premature wear or belt jump.

Aluminum alloy pulleys are well-suited for the belt tension levels typical of small-format CNC routers, 3D printers, and light robotic joints. For reference, S3M belts are rated for moderate power transmission at low-to-medium speeds. If your application involves sustained high tension, shock loads, or elevated temperatures, consider whether a steel or hardened pulley would be more appropriate. For standard maker and educational automation use cases, aluminum provides adequate strength with the benefit of reduced rotating mass.

You can mix tooth counts to create a drive ratio. For example, pairing a 30-tooth drive pulley with a 40-tooth driven pulley gives a 4:3 speed reduction (the driven shaft turns slower with more torque). The belt length must be calculated to suit the center distance and the sum of the two pulley pitch circumferences. Many online belt length calculators accept tooth count and center distance as inputs. If you are replacing an existing pulley, match the tooth count exactly to maintain your original drive ratio.

Yes, a set screw is included with each pulley. Set screws on pulleys of this size typically require a 1.5 mm, 2 mm, or 2.5 mm hex (Allen) key — the exact size depends on the specific variant. A standard metric hex key set will cover all sizes in this range. Tighten the set screw firmly against the shaft flat or shaft surface, but avoid overtightening, which can strip the thread in the aluminum hub.