Lab Inventory: Timing Belts and Pulleys¶

Timing belts and pulleys are toothed belts and pulleys used in motion transmission. For a general introduction, please see Timing Belt Guide.

The following tables may help you identify commonly used parts we have available in the lab supply. We currently prefer metric GT2 parts which have a 2 mm belt pitch, although some inch-size stock can still be found in the lab.

For a searchable index of all lab parts, please see Physical Computing Lab Inventory.

GT2 Timing Belts¶

Timing belts are either open-ended segments or closed “endless” belts with a specific number of teeth. Linear drive systems typically use open-ended belts, but transmissions typically use endless belts between pairs of pulley.

We are only able to stock a few specific sizes of endless belts so transmission ratios and pulley spacing need to be designed around the available parts.

All of the GT2 belts we stock are 6 mm width. The open-ended segments typically come in 10 meter lengths but may have been cut shorter.

The key parameters of our GT2 endless belts are the tooth count and the width, e.g. a 150 tooth belt with 6 mm width is designated as “150T x 6 mm”. The length of a endless belt is the pitch multiplied by the tooth count. E.g., a 150T belt is 300 mm in circumference measured along the pitch line.

Endless GT2 Belts¶
Size	Lab Part #	Source
110T x 6 mm	proposed	included in kit: Amazon
150T x 6 mm	proposed	ten-pack: Amazon
200T x 6 mm	proposed	included in kit: Amazon
300T x 6 mm	proposed	included in kit: Amazon
400T x 6 mm	proposed	included in kit: Amazon
610T x 6 mm	proposed	included in kit: Amazon

GT2 Timing Pulleys¶

The key parameters of our GT2 pulleys are the tooth count and the bore size. E.g. a 20 tooth pulley with 5 mm bore is designated as “20T x 5 mm”.

4 mm bore size fits our small 25 mm gearmotors
5 mm bore size fits our NEMA17 steppers
6 mm bore size fits our goBILDA large gearmotors
8 mm bore size typically needs a non-stocked shaft or motor or a custom adapter

We stock commonly available small pulleys principally intended for mounting directly on motor shafts. In general, larger sizes can be fabricated as custom pulleys on the laser-cutter or 3D printer. This is also the only way to achieve very large diameter pulleys.

GT2 Timing Pulleys with 4 mm bore¶
Size	Lab Part #	Source
16T x 4 mm	proposed	possible source: Amazon
20T x 4 mm	proposed	possible source: Amazon

GT2 Timing Pulleys with 5 mm bore¶
Size	Lab Part #	Source
16T x 5 mm	proposed	possible source: Amazon
20T x 5 mm	included in Lab Part 1875	possible source: Amazon
40T x 5 mm	proposed	possible source: Amazon
80T x 5 mm	non-stock	possible source: Amazon

GT2 Timing Pulleys with 6 mm bore¶
Size	Lab Part #	Source
16T x 6 mm	non-stock	possible source: Amazon
20T x 6 mm	non-stock	possible source: Amazon

GT2 Pulley Axles and Bushings¶

Most of our pulleys are intended to mount directly on a motor shaft, and in general we recommend fabricating your our pulley profile to drive the load. However, the stock pulleys can be used as idlers if installed on a short 4 or 5 mm shaft turning on bushings.

GT2 Kits¶

Many of our timing belts and pulley parts are purchased as kits which include multiple parts. These are often sold for repair or construction of 3D printers.

A typical kit is Lab Part 1875, previously available from Amazon, which includes:
- 10 meters of open-ended 6 mm GT2 belt
- eight 20T x 5 mm GT2 pulleys (6 mm width, 5 mm bore)
- four belt tensioner springs
- set screws and a hex wrench
A proposed belt kit from Amazon includes five GT2 endless 6 mm belts with 110, 200, 300, 400, and 610 teeth.

Round Belts¶

Round belts are flexible round cord or tube which can be used for motion transmission. The belts have a smooth surface so they can drift, meaning the transmission ratios are not precisely guaranteed. However, they offer smooth motion and may be more visually appealing.

The lab stocks open-ended round tubular belting which can be used to create custom endless belts by joining a custom length. The lab does not stock any round belt pulleys, but the following can be used with a custom 3D-printed pulley:

Lab Part 1877, clear hollow-core round belting, 3/16 inch diameter, for use with minimum 1.5 inch pulley diameter.

XL Timing Belts¶

Inch-sized XL timing belts have 0.200 inch pitch (5.08 mm). The teeth are distinctly larger than GT2.

The following XL belts were previously stocked but are now discontinued:

MXL Timing Belts¶

Inch-sized MXL timing belts have 0.080 inch pitch (2.032 mm). These look very similar to GT2 belts but are not quite compatible.