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When your DIY drive system, robotics project, or light-duty machine demands reliable belt tracking without slippage, a poorly matched pulley becomes the weakest link. These V-grooved aluminum pulleys are engineered specifically for 4mm round belts, giving hobbyists, prototype builders, and small-machine designers a drop-in solution that holds belt alignment under continuous rotation.
Each pulley is machined from aluminum alloy with a consistent V-groove profile sized for 4mm round belts. The bore diameter is 4mm across all variants. Outer diameters span 16mm, 20mm, 30mm, 40mm, and 50mm (approximately 0.63"–1.97"), with groove widths ranging from 4mm to 12mm (approximately 0.16"–0.47") depending on the selected size. The aluminum construction keeps rotating mass low while providing adequate rigidity for the intended load range.
Typical use cases include small conveyor belt systems for maker projects, tension-controlled round-belt drives in 3D printer or CNC auxiliary axes, and lightweight power transmission in educational robotics kits. The range of OD options also makes these pulleys well-suited for custom gear-ratio configurations in tabletop automation and DIY motorized mechanisms.
Machined from aluminum alloy for a low-mass, corrosion-resistant pulley body that reduces rotational inertia in speed-sensitive drive systems.
The groove geometry is matched to 4mm round belts, maintaining consistent belt seating and reducing lateral drift during operation.
Five outer diameter options — 16mm, 20mm, 30mm, 40mm, and 50mm — allow you to dial in the exact drive ratio your project requires.
Uniform 4mm bore fits standard small shafts and motor output shafts. Groove width variants (4mm–12mm) accommodate different belt lengths and tension setups.
The aluminum body keeps pulley weight typically under 30g for smaller ODs, making these suitable for motors with limited torque output in robotics and automation rigs.
The 4mm bore is machined to accept a standard 4mm shaft. Pair with a set screw or shaft collar (sold separately) for secure axial retention.
| Material | Aluminum alloy |
|---|---|
| Belt Type Compatibility | 4mm round belt |
| Bore Diameter | 4mm (0.157") |
| Outer Diameter (OD) | 16mm / 20mm / 30mm / 40mm / 50mm (0.63"–1.97") |
| Groove Width | 4mm – 12mm (see variant options) |
| Hub / Body Thickness | 4mm (0.157") |
| Surface Finish | See variant options |
| Weight (per piece) | See variant options |
| Packing Quantity | 1 piece per unit (multi-pack options available) |
These pulleys are designed exclusively for 4mm round belts. The V-groove profile is sized to seat a 4mm circular cross-section belt. They are not compatible with flat belts, V-belts with trapezoidal profiles, or timing/toothed belts.
The OD determines your drive ratio when paired with a second pulley. A larger OD on the driven pulley reduces output speed and increases torque; a smaller OD does the opposite. Measure the center-to-center shaft distance in your build and calculate the required belt length before selecting OD. Available options are 16mm, 20mm, 30mm, 40mm, and 50mm.
The groove width (the second number in the size designation, e.g., "20mm x 6mm x 4mm") refers to the width of the V-groove channel. For a standard 4mm round belt, a groove width of 4mm–6mm provides a snug fit. Wider groove widths (8mm–12mm) allow more belt travel clearance and can be useful in applications with slight belt misalignment or where the belt needs to float laterally.
Aluminum alloy has inherent oxidation resistance — it forms a thin oxide layer that protects the base metal from further corrosion. These pulleys are suitable for indoor environments with moderate humidity. For outdoor or high-moisture applications, consider applying a light coating of machine oil or using an anodized variant if available.
The 4mm bore is machined to slide onto a 4mm shaft. Axial and rotational retention depends on your mounting method — a set screw collar, retaining clip, or adhesive bonding (for non-removable installations) are common approaches. Set screws and shaft collars are not included and must be sourced separately.
Yes. Because all variants share the same 4mm bore, you can stack or sequence pulleys across multiple shafts to create compound drive ratios. Ensure adequate belt tension and shaft alignment at each stage. The range of OD options (16mm–50mm) gives you a maximum single-stage ratio of approximately 3.1:1 using the 16mm and 50mm pulleys together.
Yes. The lightweight aluminum construction and precise V-groove profile make these a practical choice for auxiliary belt drives on 3D printers (e.g., filament feeders, bed leveling mechanisms) and CNC machine accessory axes where round belt drives are used. Confirm that your belt loop length matches the pulley OD and center distance before assembly.
