XL Timing Belt Pulley Keyway Bore,BF/K 15T 16T 18T 24T 25T For CNC, 3D Printer

BF-type pulleys have flanges on both sides of the tooth profile, which physically retain the belt and prevent it from walking off the pulley during operation. Choose BF-type when your belt has no other lateral guide. K-type pulleys are unflanged — use them when your machine frame, tensioner, or mating pulley already provides belt tracking, or when you need to slide the belt on axially during assembly.

XL stands for Extra Light and refers to a trapezoidal tooth profile with a 5.080mm (0.200 inch) pitch — the distance between adjacent tooth centers. These pulleys are compatible with any standard XL-pitch timing belt in 10mm, 15mm, or 20mm widths. Do not use with T5, GT2, or other pitch standards, as the tooth profiles are not interchangeable.

Measure your motor or drive shaft diameter with calipers. For standard round-hole bores, the bore should match the shaft diameter exactly — a loose fit will cause runout and lost motion. For keyway bores, also confirm the keyway width and depth on your shaft matches the keyway spec listed in the variant name (e.g., 4×1.8mm means 4mm wide × 1.8mm deep). Common stepper motor shaft sizes are 5mm, 6.35mm (1/4 in), and 8mm.

These aluminum alloy pulleys are suited for the torque and speed ranges typical of NEMA 17 and NEMA 23 stepper-driven CNC routers and 3D printers operating at standard rapid traverse rates. For heavy-duty servo-driven machines with high continuous torque, verify the pulley's rated torque against your drive system's output. Keyway bore variants provide significantly better torque transmission than set-screw-only retention under sustained load.

The aluminum alloy body offers good resistance to oxidation in typical indoor workshop conditions. The natural anodized or machined finish provides a surface layer that slows further oxidation. Avoid prolonged exposure to cutting fluids, salt spray, or strongly acidic/alkaline environments, which can accelerate surface degradation. For outdoor or high-humidity enclosures, consider applying a light protective coating.

Yes — pairing pulleys of different tooth counts on the same XL belt creates a mechanical drive ratio. A 15T driver paired with a 25T driven pulley produces a 1:1.67 reduction, increasing torque while reducing speed. Ensure both pulleys share the same belt pitch (XL) and the same belt width. Also verify that your center distance and belt length accommodate the chosen tooth counts.

For 3D printers using XL belts, 15T–18T pulleys are common on direct-drive or Bowden extruder motor shafts, providing a good balance of resolution and speed. For CNC router X/Y axes, 18T–25T pulleys are typical, offering higher linear speed per motor revolution. Match your tooth count to your existing belt loop length and desired steps-per-mm calculation for your motion controller firmware.