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When your belt drive slips, wobbles, or simply lacks a reliable guide point, the root cause is often a poorly matched pulley. Hobbyists, makers, and light-machinery builders who work with PU round belts need a fixed pulley that holds its bore tight, seats the belt cleanly in the groove, and stays put under continuous rotation. This aluminum single-groove U pulley is machined to deliver exactly that — consistent belt tracking without the guesswork.
Each pulley is machined from aluminum alloy, giving it a lightweight yet rigid body. The outer diameter spans 20 mm to 80 mm (approximately 0.79 in to 3.15 in), and the U-shaped groove width ranges from 4 mm to 8 mm (0.16 in to 0.31 in) to match common PU round belt cross-sections. Bore sizes run from 5 mm to 15 mm (0.20 in to 0.59 in), covering a wide range of shaft diameters found in DIY and light-industrial setups.
Typical applications include small conveyor systems where a fixed idler pulley is needed to maintain belt tension, desktop CNC or laser-cutter belt routing where a single-groove aluminum pulley keeps the drive loop aligned, and 3D printer or automation prototype builds that use PU round belt transmission to transfer motion between shafts.
Machined from aluminum alloy for a rigid yet lightweight build that reduces rotational inertia in low-load belt drive systems.
Available in six outer diameters — 20, 30, 40, 50, 60, and 80 mm — so you can match the pulley ratio your drive requires without custom machining.
Groove widths of 4 mm, 5 mm, 6 mm, and 8 mm (OD-dependent) seat PU round belts securely and prevent lateral belt walk during operation.
Bore options from 5 mm to 15 mm let you fit the pulley directly onto standard metric shafts without additional adapters in most cases.
Solid fixed-hub construction keeps the pulley stationary on the shaft, making it suitable for use as a drive pulley or a fixed idler in tensioning setups.
Compact dimensions and standard metric bores make these pulleys straightforward to integrate into maker projects, automation rigs, and small conveyor prototypes.
| Material | Aluminum alloy |
|---|---|
| Pulley Type | Single groove, fixed hub |
| Groove Profile | U-groove |
| Outer Diameter (OD) | 20 mm / 30 mm / 40 mm / 50 mm / 60 mm / 80 mm |
| Groove Width | 4 mm / 5 mm / 6 mm / 8 mm (varies by OD variant) |
| Bore Size | 5 mm / 6 mm / 7 mm / 8 mm / 9 mm / 10 mm / 11 mm / 12 mm / 13 mm / 14 mm / 15 mm |
| Compatible Belt Type | PU round belt |
| Hub Style | Fixed (set screw recommended for shaft retention) |
| Surface Finish | See variant options |
| Weight | See variant options |
| Item Quantity | 1 pcs per order (multi-pack options available) |
The outer diameter determines your pulley ratio. If you need a 2:1 speed reduction, pair a 40 mm driven pulley with a 20 mm drive pulley. Measure the center-to-center shaft distance and available belt length first, then select OD values that give you the ratio you need while keeping belt wrap angle above roughly 120°.
The groove width should be equal to or very slightly larger than the diameter of your PU round belt. For example, a 4 mm diameter PU round belt fits a 4 mm groove width. Using a groove that is too wide allows the belt to shift laterally; too narrow and the belt will ride on the groove edges rather than seating properly.
Measure your shaft diameter with a caliper. Select the bore size that matches your shaft exactly — for example, a 6 mm shaft requires the 6 mm bore option. If you plan to use a set screw to lock the pulley, ensure the bore-to-shaft fit is snug (H7/h6 tolerance range is typical for this type of application).
Aluminum alloy has natural oxidation resistance suitable for indoor and dry environments. For applications exposed to moisture, light misting, or mild chemicals, the aluminum surface will form a protective oxide layer. For harsh outdoor or wet environments, consider applying a compatible protective coating or selecting a stainless steel pulley instead.
Yes. Because this is a fixed-hub pulley (not a bearing-mounted idler), it is best used as a drive pulley mounted on a rotating shaft. If you need a true idler that spins freely on a stationary bolt, you would need to add a bearing between the bore and the bolt. For simple fixed-point belt routing, it works well as a guide pulley when mounted on a shaft that rotates with the belt.
These pulleys are designed for light-duty and prototype applications typical of PU round belt drives — such as small conveyors, 3D printers, desktop automation, and maker projects. They are not rated for heavy industrial loads. Exact load capacity depends on the OD, bore, shaft support, and belt tension in your specific setup. Contact us to confirm suitability for your application.
The pulley slides onto your shaft via the bore. To prevent axial movement and rotation on the shaft, you will typically need a set screw (grub screw) tightened against the shaft, or a shaft collar on each side. A keyway arrangement can also be used if your shaft has a key slot. These fastening components are not included and are sold separately.
