# GT2 idler pulleys, toothed and smooth: 16T / 20T, 3 and 5 mm bore, OD, width, F623 / F625 bearing sizes

> What are the dimensions of a GT2 idler pulley (16T or 20T, toothed or smooth) and which bearing does it use?

- Category: Hardware › Bearings, rails & motion
- Kind: Standard part
- Basis: Seller and maker product pages (Tinytronics, Systeal, Filastruder, Printed Solid); bearing sizes from the existing F-series bearing page (NSK, skdin, kugellager-express)
- Page: https://xemstudio.com/objects/gt2-idler-pulleys-toothed-smooth/ · JSON: https://xemstudio.com/api/geometry?object=gt2-idler-pulleys-toothed-smooth · Plain text: https://xemstudio.com/objects/gt2-idler-pulleys-toothed-smooth/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files CC BY 4.0 or their publisher's license
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** True size, with no tolerance added.

## Notes

- A GT2 idler is a pulley (toothed or smooth) on a ball bearing, so it spins on a fixed screw or shaft. Toothed idlers have the same teeth as a pulley (16T and 20T are the common ones) and run on the toothed side of the belt; smooth idlers run on the back of the belt. The table is what sellers and Gates print; every row is one product. 'OD' is the shop's own 'outer diameter': for the 16T and 20T it is larger than the tooth OD (9.68 and 12.22 mm by the GT2 rule, see the GT2 pulley page), so it can only be the flange. Printed Solid's Gates smooth idler is a 12 mm OD with no flange stated.
- The bearing behind it: the idler bores 3 and 5 mm are the bores of 623 (3 x 10 x 4) and 625 (5 x 16 x 5) bearings, which the flanged-bearing page lists with their flanges (F623 flange 11.5 x 1, F625 flange 18 x 1). None of the sources read says which bearing a given idler holds or how many (Systeal says 'dual bearing' without a size), so the table does not pair them.
- Widths differ: Tinytronics prints 8.5 mm for all six, Filastruder 10 mm outside flange to outside flange for its 6 mm-belt idler. Different makers, so different widths: measure the one you buy.
- No files: no source read gives a full outline (tooth OD, flange thickness, bearing pocket, hub) for any idler, so a model would be invented. Use the bearing pages for the pocket and the pulley page for the tooth Ø.

## Sizes

| type | product | teeth | bore, mm | OD as printed, mm | width, mm | belt width, mm |
|---|---|---|---|---|---|---|
| toothed, bearing | Tinytronics GT2316T | 16 | 3 | 13 | 8.5 | 6 |
| toothed, bearing | Tinytronics GT2320T | 20 | 3 | 18 | 8.5 | 6 |
| toothed, bearing | Tinytronics GT2520T | 20 | 5 | 18 | 8.5 | 6 |
| smooth, bearing | Tinytronics GT2316S | 16 (same Ø as 16T) | 3 | 13 | 8.5 | not fully stated |
| smooth, bearing | Tinytronics GT2320S | 20 (same Ø as 20T) | 3 | 18 | 8.5 | not fully stated |
| smooth, bearing | Tinytronics GT2520S | 20 (same Ø as 20T) | 5 | 18 | 8.5 | not fully stated |
| toothed, dual bearing | Systeal GT2-ID-PULLEY-D5-6W | 20 | 3 or 5 | 18 | — | 6 |
| toothed, bearing | Filastruder (Gates 2GT idler), 6 mm belt version | 20-tooth equivalent | 3 or 5 | — | 10 (flange to flange) | 6 |
| smooth | Printed Solid, Gates PowerGrip 2GT smooth idler | 20-tooth equivalent | 5 | 12 | — | — |
| bearing | 623 / F623 | 3 x 10 x 4 |  | F623: flange 11.5 x 1 |  | idler for 16T / 20T on a 3 mm bore |
| bearing | 625 / F625 | 5 x 16 x 5 |  | F625: flange 18 x 1 |  | idler on a 5 mm bore, 16 mm bearing OD |

## Where the files are

- Tinytronics: [GT2 idler pulleys: toothed and toothless, bore, outer diameter, height, belt width](https://www.tinytronics.nl/en/mechanics-and-actuators/parts/pulleys) — web — Publisher's page; dimensions are facts
- Systeal: [GT2 dual-bearing idler timing pulley, 20 teeth, bore 3 or 5, 6 mm belt, OD 18](https://www.systeal.com/en/pulleys-and-belts/1893-gt2-dual-bearing-idler-timing-pulley-belt-width-6mm.html) — web — Publisher's page; dimensions are facts
- Filastruder: [Gates 2GT idler: 6 mm belt idlers are 10 mm wide outside flange to outside flange; bore 5 or 3](https://filastruder.com/products/gates-2gt-idler) — web — Publisher's page; dimensions are facts
- Printed Solid: [Gates PowerGrip 2GT smooth idler: OD 12 mm, 5 mm bore](https://www.printedsolid.com/collections/e3d/products/gates-powergrip-2gt-smooth-idler) — web — Publisher's page; dimensions are facts

## Questions

**What size is a GT2 smooth idler?**

Common smooth idlers are 13 mm (16-tooth equivalent) and 18 mm (20-tooth equivalent) outer diameter, 8.5 mm tall (Tinytronics); Gates' 2GT smooth idler is 12 mm with a 5 mm bore.

**What bearing does a GT2 idler use?**

3 mm bore idlers match the 623 / F623 (3 x 10 x 4); 5 mm bore idlers match the 625 / F625 (5 x 16 x 5). The sellers read do not state which one they fit.

**How wide is a GT2 idler for a 6 mm belt?**

10 mm outside flange to outside flange on Filastruder's Gates idler; 8.5 mm on Tinytronics' idlers.

## Fits with

- [GT2 timing pulleys 18T to 60T: pitch and outside diameter, flange, bores 5 / 6 / 8 mm, 6 and 9 mm belts (+ 64 to 80T diameters)](https://xemstudio.com/objects/gt2-timing-pulleys-18-60t-bores/)
- [GT2 timing pulleys, 16T–60T (2 mm pitch)](https://xemstudio.com/objects/gt2-pulleys/)
- [Flanged ball bearings F6xx and MF: F623, F624, F625, F688, F695, F608 and more: bore, OD, width, flange diameter and thickness](https://xemstudio.com/objects/flanged-ball-bearings-f6xx-mf/)
- [Ball bearings, 683 to 6210 and flanged F6xx (ISO 15)](https://xemstudio.com/objects/ball-bearings-metric/)
- [GT2 (2GT) closed-loop timing belts, 6 mm wide: standard lengths and tooth counts, 110 to 1524 mm](https://xemstudio.com/objects/gt2-closed-loop-belt-lengths/)