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When your motion control build demands repeatable, slip-free power transmission, a mismatched or poorly machined pulley becomes the weakest link in the entire drivetrain. Engineers, CNC builders, and robotics hobbyists who need a reliable S3M timing belt pulley with a keyed bore will find this series covers the widest range of tooth counts and bore sizes in a single listing — eliminating the frustration of sourcing multiple SKUs.
Each S3M timing belt pulley in this series features a 3 mm pitch (S3M profile), a 16 mm belt-contact width, and a precision-machined step/keyway bore. Tooth counts range from 65T to 150T, with bore diameters available from 8 mm (0.31 in) to 25 mm (0.98 in). Keyway dimensions scale with bore size: 3×1.4 mm for smaller bores up to 8×3.3 mm for larger bores, ensuring a secure shaft-to-hub connection without set-screw slippage.
Typical applications include CNC router X/Y axis drives, 3D printer extruder and gantry systems, light-duty conveyor indexing, and desktop robotic arm joints — anywhere a synchronous S3M drive pulley with a keyed bore is required for accurate positioning and repeatable motion.
| Belt Profile | S3M (Synchronous, 3 mm pitch) |
|---|---|
| Pitch | 3 mm |
| Belt Width | 16 mm |
| Number of Teeth | 65T / 70T / 72T / 75T / 80T / 90T / 100T / 120T / 140T / 150T |
| Bore Diameter | 8 mm / 10 mm / 12 mm / 14 mm / 15 mm / 17 mm / 19 mm / 20 mm / 25 mm |
| Keyway Dimensions | 3×1.4 mm / 4×1.8 mm / 5×2.3 mm / 6×2.8 mm / 8×3.3 mm (varies by bore) |
| Hub Style | Step hub with keyway |
| Material | See variant options |
| Finish / Colour | See variant options |
| Outer Diameter | See variant options |
| Quantity per Pack | 1 Pcs |
The tooth count determines the pulley pitch diameter and, combined with your motor pulley, sets the drive ratio. Divide the driven pulley teeth by the drive pulley teeth to get the reduction ratio. For example, pairing a 20T motor pulley with an 80T load pulley gives a 4:1 reduction. Use the tooth count selector above to match your required ratio.
Measure your motor shaft diameter with a caliper. NEMA 23 stepper shafts are typically 8 mm, and larger servo motors often use 10–25 mm shafts. Select the bore that matches your shaft diameter exactly — the keyway provides the positive drive connection, so a snug bore fit is important.
The keyway dimension is expressed as width × depth. A 5×2.3 mm keyway accepts a standard 5 mm wide key that sits 2.3 mm deep into the hub. The mating key must match both the shaft keyway and the pulley keyway dimensions. Keyway size is automatically matched to bore size in this listing.
Yes. This pulley is designed for S3M profile synchronous timing belts with a 3 mm pitch and 16 mm width. Ensure your belt is also rated for 16 mm width. S3M belts are widely available in both open-end and closed-loop configurations.
A properly fitted key and keyway provides a positive mechanical lock between shaft and pulley, transmitting torque through shear rather than friction alone. This is significantly more reliable than set-screw-only hubs for continuous or reversing loads. Ensure the key is the correct size and that the bore fits the shaft with minimal clearance for best results.
Yes — S3M pulleys are commonly used in CNC router gantry drives, 3D printer Z-axis drives, and desktop automation systems. The 16 mm belt width provides good load capacity for these applications. Confirm your existing belt profile is S3M (3 mm pitch) before ordering, as S3M is not interchangeable with GT2, HTD 3M, or other 3 mm pitch profiles.
Both S3M and HTD 3M have a 3 mm pitch, but the tooth profile differs — S3M uses a trapezoidal tooth while HTD 3M uses a curvilinear (rounded) tooth. They are not interchangeable. Always match the pulley profile to your belt profile exactly.
