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When your belt-drive project demands consistent tracking and slip-free power transfer, a poorly matched pulley becomes the weakest link. Engineers, robotics builders, and CNC hobbyists who rely on PU round belts need a pulley that holds tight tolerances and resists wear across thousands of cycles — that's exactly where these U grooved pulleys deliver.
Each U grooved pulley is machined from aluminum alloy, featuring a clean U-profile groove with a fixed 3mm groove width designed to seat standard PU round belts securely. Outer diameters span 15mm to 30mm (0.59 in to 1.18 in), with bore diameters ranging from 2mm to 15mm (0.08 in to 0.59 in) to fit a wide range of motor shafts and axles. Available in single-groove, double-groove, and triple-groove configurations to match your drive ratio and belt-count requirements.
These aluminum U groove pulleys are well-suited for small-scale conveyor systems requiring smooth round-belt tracking, desktop CNC machines and laser cutters using PU belt drives, and robotics platforms where compact, lightweight pulleys reduce rotational inertia. The anodized aluminum construction keeps weight low while maintaining the dimensional stability needed for repeatable positioning in maker and automation projects.
Machined aluminum body keeps rotational mass low while providing the rigidity needed for consistent belt tracking in continuous-duty applications.
Groove width precisely matched to standard 3mm PU round belts, preventing lateral belt wander and reducing premature belt wear.
Choose single-groove for simple drives, double-groove for redundancy or dual-belt layouts, or triple-groove for high-torque multi-belt configurations.
Four outer diameter options (15mm / 20mm / 25mm / 30mm) let you dial in the exact drive ratio your project requires without custom machining.
Sixteen bore diameter options — from 2mm up to 15mm (including 3.17mm and 6.35mm for imperial shafts) — cover the most common motor and axle shaft sizes.
Small form factor suits space-constrained builds such as desktop CNC gantries, robotic arms, and compact conveyor modules where every gram matters.
| Material | Aluminum alloy |
|---|---|
| Groove Profile | U-groove (round belt) |
| Groove Width | 3mm |
| Outer Diameter (OD) | 15mm / 20mm / 25mm / 30mm (0.59–1.18 in) |
| Bore Diameter | 2 / 3 / 3.17 / 4 / 5 / 6 / 6.35 / 7 / 8 / 9 / 10 / 11 / 12 / 13 / 14 / 15mm |
| Groove Count | Single / Double / Triple |
| Compatible Belt | PU round belt, 3mm diameter |
| Finish | See variant options |
| Weight | See variant options |
| Quantity per Order | 1 piece |
Drive ratio equals the driven pulley OD divided by the driving pulley OD. For example, pairing a 15mm drive pulley with a 30mm driven pulley gives a 2:1 reduction. Select your OD based on the speed reduction or increase your application requires, then confirm the bore matches your motor shaft.
These pulleys are designed specifically for 3mm-diameter PU (polyurethane) round belts. The U-profile groove seats the round belt securely. Do not use flat belts or V-belts, as the groove geometry will not provide proper engagement.
Measure your motor or axle shaft diameter precisely with calipers. Select the bore that matches your shaft. Note that 3.17mm corresponds to 1/8 inch and 6.35mm corresponds to 1/4 inch — common imperial shaft sizes used in many hobby motors and stepper motors.
Double-groove pulleys allow you to run two parallel belts simultaneously, which increases load capacity or provides redundancy. Triple-groove pulleys are suited for high-torque applications or multi-belt drive systems. For most light-duty robotics and CNC builds, a single-groove pulley is sufficient.
Aluminum alloy offers good natural corrosion resistance for indoor and dry environments. For applications exposed to moisture or mild chemicals, the anodized surface finish provides additional protection. These pulleys are not recommended for submerged or highly corrosive environments without additional sealing.
Shaft retention method depends on the specific variant. Many aluminum pulleys of this type use a set screw (grub screw) to clamp onto the shaft. Confirm your variant includes a set screw or plan to use a press-fit or adhesive retention method appropriate for your torque requirements.
Yes. The tight OD tolerances and consistent groove profile make these pulleys suitable for desktop CNC routers, laser cutters, and 3D printer extruder drives that use PU round belts. Pair with matching idler pulleys and tensioners for best tracking performance.
