Timing Pulley S3M 15T~28T for 10mm Belt Aluminum AF Shape Timing Pulley ID=4~15

The tooth count determines your drive ratio. Divide the driven pulley teeth by the driving pulley teeth to get the ratio. For example, a 20 T driver paired with a 20 T driven pulley gives a 1:1 ratio. For speed reduction, use a smaller driver and larger driven pulley. This listing covers 15 T to 28 T — select the combination that matches your target ratio.

Match the bore diameter to your motor or shaft OD. Common stepper motor shaft sizes are 5 mm and 6.35 mm (1/4 in); servo motors often use 8 mm or 10 mm shafts. If your shaft is imperial (e.g., 1/4 in = 6.35 mm, 1/2 in = 12.7 mm), select the corresponding bore option in the variant selector above.

A keyway is recommended when the pulley must transmit significant torque or when the shaft direction reverses frequently (e.g., CNC axes). Without a keyway, the pulley is held by a set screw alone, which can slip under high load. Choose the keyway width that matches the key already cut on your shaft — typically 3 mm for 8 mm bores, 4 mm for 10–12 mm bores, and 5 mm for 12.7–15 mm bores. Confirm your shaft's key specification before ordering.

Yes. The S3M tooth profile is an industry-standard specification (3 mm pitch, curvilinear tooth form). These pulleys are compatible with any S3M synchronous belt of 10 mm width, regardless of brand, as long as the belt pitch and width match.

Aluminum alloy pulleys offer an excellent strength-to-weight ratio and are the standard choice for CNC machines, 3D printers, and light-to-medium automation where minimizing rotating mass improves acceleration and reduces motor load. For very high-torque industrial drives or abrasive environments, steel pulleys may be preferred. For typical DIY and maker applications with S3M belts, aluminum is more than adequate.

Aluminum naturally forms a thin oxide layer that acts as a protective barrier against further corrosion in most indoor environments. For outdoor or high-humidity applications, consider applying a light coat of dry lubricant or corrosion inhibitor. The natural (uncoated) finish is suitable for the vast majority of workshop and lab automation uses.

Yes. Select the "without keyway & 2" or the keyway + 2 pcs option in the Keyway width & Qty(pcs) variant selector to receive two pulleys of the same tooth count and bore in one order — ideal for building a complete drive pair at a lower per-unit cost.