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When a misaligned or slipping timing belt derails your CNC router mid-cut or causes layer shifts in a 3D print, the culprit is often a poorly fitted idler pulley. Engineers, makers, and automation builders who demand repeatable motion need idler pulleys that hold their position, grip the belt profile cleanly, and accept a wide range of shaft sizes without custom machining. These HTD3M 20mm idler timing drive pulleys are designed exactly for that use case.
Each pulley is machined from aluminum alloy with a flanged outer rim to keep the HTD 3M belt tracking true. The tooth width is 20mm (approximately 0.79 in), and the overall flange width is 21mm (approximately 0.83 in). Bore options span 4mm to 25mm (approximately 0.16 in to 0.98 in), and tooth counts range from 20 to 60 teeth, giving you precise pitch-diameter control across a wide range of drive ratios and belt-wrap angles.
Typical applications include idler and tensioner positions on HTD 3M belt-driven CNC gantries, CoreXY and Cartesian 3D printer motion systems, light-duty conveyor tensioners, and robotic arm joint drives where smooth, low-backlash belt routing is critical.
Available from 4mm to 25mm bore diameter, covering the most common motor and idler shaft sizes used in CNC and 3D printing builds without additional machining.
The curved HTD tooth form distributes belt load across a larger contact area than trapezoidal profiles, reducing tooth stress and extending belt life in continuous-duty applications.
Choose from 20, 22, 24, 25, 26, 28, 30, 32, 34, 35, 36, 38, 40, 50, or 60 teeth to dial in the exact pitch diameter and belt-wrap angle your drive system requires.
Integrated flanges on both sides of the tooth face keep the HTD 3M belt centered on the pulley under lateral loads, preventing belt walk and unplanned derailment.
Machined aluminum body keeps rotating mass low for responsive acceleration in servo and stepper-driven axes while providing adequate strength for light-to-medium duty loads.
Designed for use without a drive key — ideal for idler and tensioner positions where the pulley spins freely on a fixed shaft or bearing, maintaining belt tension without transmitting torque.
| Belt Type | HTD 3M (3mm pitch) |
|---|---|
| Tooth Width | 20mm (0.79 in) |
| Flange Width | 21mm (0.83 in) |
| Number of Teeth | 20 / 22 / 24 / 25 / 26 / 28 / 30 / 32 / 34 / 35 / 36 / 38 / 40 / 50 / 60 (see variant options) |
| Bore Diameter | 4 / 5 / 6 / 6.35 / 8 / 10 / 12 / 12.7 / 14 / 15 / 17 / 19 / 20 / 25mm (see variant options) |
| Material | Aluminum alloy |
| Finish | Natural / anodized (see variant options) |
| Quantity per Order | 1 piece |
| Bore Securing Method | Set screw (see variant options) |
| Outer Diameter | See variant options |
| Hub Length | See variant options |
The number of teeth determines the pitch diameter of the pulley (pitch diameter = teeth × pitch / π). For idler and tensioner use, the tooth count affects belt-wrap angle and the minimum bend radius the belt experiences. A higher tooth count means a larger diameter and gentler belt curvature, which is better for belt longevity. Match the tooth count to the space available in your drive system and ensure the pitch diameter is large enough to avoid over-bending the belt.
Select the bore that matches your idler shaft or bearing outer diameter. Common choices are 5mm and 8mm for 3D printer idler pins, and 6mm, 8mm, or 10mm for CNC gantry idler shafts. If you plan to mount the pulley on a bearing, measure the bearing's outer diameter and choose the matching bore. For shaft-mounted use with a set screw, the bore should match the shaft diameter exactly.
Yes. These pulleys are machined to the HTD 3M tooth profile with a 3mm pitch and a 20mm tooth width. They are compatible with any standard HTD 3M timing belt that is 20mm wide. Do not use with MXL, GT2, or other belt profiles — the tooth geometry is not interchangeable.
The aluminum alloy construction provides adequate strength for light-to-medium duty idler and tensioner applications such as CNC routers, 3D printers, and small robotic joints. For heavy industrial conveyor or high-torque drive applications, verify the load against the material's yield strength. As idler pulleys, they do not transmit torque, so the primary load is radial belt tension.
Aluminum alloy naturally forms a thin oxide layer that provides moderate corrosion resistance in typical indoor workshop and lab environments. For humid or outdoor environments, an anodized finish variant offers improved surface protection. Avoid prolonged exposure to salt spray or strong acids without additional protective coating.
These pulleys are designed primarily for idler and tensioner use. They can be used as drive pulleys if secured firmly to a shaft with the set screw, but they do not include a keyway. For high-torque drive applications, a keyed drive pulley is recommended to prevent slipping under load. For low-torque or light-duty drives, the set screw may be sufficient — assess your torque requirements before use.
The 6.35mm bore corresponds to 1/4 inch, which is a common shaft size in imperial-standard hardware and some stepper motors. If your shaft is metric 6mm, choose the 6mm bore. If your shaft is 1/4 inch (imperial), choose 6.35mm. Using the wrong bore will result in either a loose fit or an inability to mount the pulley.
