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When your CNC router, 3D printer, or robotics project demands a reliable, slip-free belt drive, mismatched pulleys are the first point of failure. Engineers, makers, and automation builders who work with round PU belts need a pulley that holds groove geometry tightly and mounts without play — this U grooved aluminum pulley is built for exactly that.
Each pulley is machined from aluminum alloy with a clean U-shaped groove sized for either 4 mm or 5 mm round PU belts. Outer diameters span 20 mm to 80 mm (approximately 0.79 in to 3.15 in), and bore diameters range from 3 mm to 20 mm (approximately 0.12 in to 0.79 in), covering the most common shaft sizes used in light-duty drive systems. The compact, single-piece body keeps rotating mass low while maintaining dimensional accuracy.
Typical applications include open-loop and closed-loop belt conveyors for tabletop automation, axis drives on desktop CNC machines, tensioner and idler positions in 3D printer motion systems, and custom robotic arm joints where a round-belt drive reduces backlash compared to chain or gear alternatives.
Available in groove widths for both 4 mm and 5 mm round PU belts, letting you standardize one pulley family across multiple machine axes.
Six outer diameter steps (20, 30, 40, 50, 60, 80 mm) give you precise speed-ratio control without custom machining.
Eighteen bore sizes from 3 mm to 20 mm accommodate the most common motor and idler shaft diameters used in light-duty automation.
Machined aluminum keeps the pulley lightweight, reducing inertia on high-cycle axes while providing adequate strength for round-belt tension loads.
The groove geometry is matched to round PU belt cross-sections, keeping the belt centered and reducing lateral drift during operation.
Suitable as a drive pulley on a motor shaft or as a tensioner/idler — the bore range and compact body make it adaptable to both roles.
| Material | Aluminum alloy |
|---|---|
| Groove Type | U-groove (round belt profile) |
| Compatible Belt Width | 4 mm or 5 mm (select variant) |
| Outer Diameter (OD) | 20 / 30 / 40 / 50 / 60 / 80 mm (select variant) |
| Bore Diameter | 3 / 4 / 5 / 6 / 7 / 8 / 9 / 10 / 11 / 12 / 13 / 14 / 15 / 16 / 17 / 18 / 19 / 20 mm (select variant) |
| Finish | See variant options |
| Hub / Flange Style | See variant options |
| Set Screw | See variant options |
| Quantity per Order | 1 piece |
Measure the cross-sectional diameter of your round PU belt. If it is 4 mm, select a Groove Width/OD option starting with "4mm". If it is 5 mm, select one starting with "5mm". Using a groove that is too narrow will pinch the belt; too wide will allow lateral movement and reduce tracking accuracy.
The OD determines your drive ratio. Divide the driven pulley OD by the drive pulley OD to get the speed reduction ratio. For example, a 40 mm driven pulley paired with a 20 mm drive pulley gives a 2:1 reduction. Choose the OD combination that achieves your target speed or torque ratio.
Measure your motor or idler shaft diameter with a caliper. Select the bore diameter that matches exactly — for example, a 6 mm shaft requires the 6 mm bore option. If you plan to use a set screw or keyway adapter, confirm the hub wall thickness is sufficient for your shaft size before ordering.
These pulleys are machined from aluminum alloy and are suited for light-to-medium duty round-belt drives typical of desktop CNC machines, 3D printers, and small robotic systems. For heavy industrial loads or high-tension applications, verify that the belt tension does not exceed the structural limits of the aluminum hub and bore wall.
Aluminum naturally forms a thin oxide layer that provides moderate corrosion resistance in typical indoor environments. For humid, wet, or outdoor use, consider applying a light coating of machine oil or a corrosion inhibitor to the bore and outer surfaces. Anodized variants offer improved surface protection if available in your selected size.
Yes. The U-groove profile and bore range make these pulleys suitable for idler and tensioner positions. When used as an idler, mount the pulley on a fixed or adjustable shaft through the bore and allow it to spin freely using a bearing or bushing — the pulley body itself does not include an integrated bearing.
Check three dimensions: (1) groove width matches your belt diameter, (2) OD gives the correct drive ratio with your mating pulley, and (3) bore diameter matches your shaft. If you are prototyping, ordering one piece first to verify fit before committing to a larger quantity is a practical approach.
