Mellow GT2 20-Tooth Drive Pulley for 9/10 mm Belts and 5 mm Shaft

Mellow GT2 20-tooth drive pulley for 9 and 10 mm belts and a 5 mm shaft, manufactured from aluminium alloy. Its 11 mm-wide toothed track identifies the wider version, with a nominal overall height of 20 mm.

It transfers motor rotation to a 2 mm-pitch GT2 belt. Each pulley revolution provides a theoretical travel of 40 mm: belt width does not change this relationship.

Machining and belt engagement

Mellow highlights the tooth finish of this family. According to the manufacturer, it uses tooling supplied by Gates and achieves a surface roughness of Ra 0.4 µm. This is a Mellow-brand pulley; the stated tooling source does not make it a Gates-brand pulley.

Well-machined teeth support consistent pulley-to-belt contact. Roughness describes the surface finish, not a dimensional tolerance or an accuracy guarantee for the complete machine. To make effective use of the drive, align the track and use appropriate belt tension.

• 11 mm track: designed for the 9 and 10 mm belt widths specified by Mellow.
• Two radial set screws: secure the pulley to a 5 mm shaft.
• Side flanges: help guide the belt without replacing proper alignment.
• Aluminium body: compact, lightweight construction.

Dimensions and specifications

Dimensions are nominal. The track is 11 mm wide, but this version is selected for a 9/10 mm belt. The flange outside diameter is not the diameter that determines belt travel.

Compatibility and related accessories

An option for Cartesian or CoreXY 3D printers and other mechanisms designed for a 9 or 10 mm GT2 belt and 5 mm shaft. Also check hub height, shaft length and belt-path position: replacing a narrower pulley may require changes to brackets, spacing and the other rollers.

It can be used with the 10 mm POWGE GT2 belt. For a return path contacting the smooth belt back, consider the Mellow smooth idler for a 10 mm belt, checking its mounting diameter and support clearance.

Many NEMA 17 motors have a 5 mm shaft, but check the specific motor: NEMA 17 does not define every shaft detail. This pulley is not a free-running roller on a bolt, is not designed for a 12 mm belt and does not replace 1.5 mm-pitch profiles or HTD profiles of a different pitch.

A wider belt does not automatically increase accuracy or guarantee higher speed. The complete system must be designed for it, including anchors, rollers and tension.

Project reference: the Voron 2.4r2 uses a 20-tooth GT2 pulley for a 9 mm belt on the 5 mm secondary shaft of each Z reduction assembly. This version matches the profile, tooth count and bore, but check its 20 mm height and track position against your assembly. It is not the motor's 16-tooth pulley or the Z-axis idler; retain the design's reduction when configuring firmware.

Installation and checks

1. Switch off the machine and verify the 5 mm bore, usable shaft length and clearance for the 20 mm overall height.
2. Align the toothed track with the belt. Prevent the hub or flanges from touching the motor or mounting bracket.
3. If the shaft has a flat, direct one set screw towards it and secure both fixings without damaging their sockets.
4. Set tension after aligning the assembly; do not use excessive tension to correct a misaligned path.
5. Check the full travel by hand, then test at low speed. Ensure the belt does not rub continuously against the flanges.

Marlin, Klipper and RepRapFirmware configuration

For a direct drive, 20 teeth × 2 mm pitch = 40 mm per revolution. With a 1.8° motor and 16 microsteps: 200 × 16 / 40 = 80 steps/mm. With a 0.9° motor and 16 microsteps: 160 steps/mm. A belt width of 9 or 10 mm does not change these values.

• Marlin: example for a direct-drive X axis with a 1.8° motor at 16 microsteps: M92 X80. Save with M500 when EEPROM is enabled.
• Klipper: use rotation_distance: 40 for the corresponding motor. Configure microsteps and full_steps_per_rotation separately; account for gear_ratio if a reduction is present.
• RepRapFirmware: under the conditions of the Marlin example, use M92 X80 in config.g, with the M350 microstepping correctly configured.

These examples are not universal values for the entire printer: do not apply them to a leadscrew, extruder or geared drive without recalculation. Internal driver interpolation does not replace the microstepping configuration used in the calculation.

If you replace another 20-tooth GT2 pulley while retaining the transmission ratio, you do not need to change steps/mm or rotation distance for that reason. Changing from 16 to 20 teeth does change belt travel from 32 to 40 mm per revolution.

This is for you if

Your project uses a 9 or 10 mm GT2 belt, a 5 mm shaft and sufficient clearance for this geometry, and you want a Mellow drive pulley with documented dimensions and configuration guidance.

This is not for you if

You need a bearing-mounted roller, a pulley for an 8 mm shaft, a track for a 12 mm belt or a replacement where the available height cannot accommodate 20 mm.

Frequently asked questions

Does the same pulley fit 9 and 10 mm belts?
Yes: this is the manufacturer's 9/10 mm version, with an 11 mm nominal track. Check your assembly's alignment and belt path.

Can I widen a 6 mm drive by changing only the pulley?
Not necessarily: the belt, anchors, rollers and clearances must all accommodate the new width.

Are the motor or belt included?
No. One pulley is supplied; other components are purchased separately.

Contents: one Mellow GT2 20-tooth drive pulley for 9/10 mm belts and a 5 mm shaft.