# GT3 (3GT, 3 mm pitch) timing pulleys: pitch diameter and outside diameter, 16T to 80T

> What is the pitch diameter and outside diameter of a GT3 (3GT, 3 mm pitch) timing pulley with N teeth?

- Category: Hardware › Bearings, rails & motion
- Kind: Standard part
- Basis: PD = 3 N / pi; OD = PD − 0.762 mm, checked on two 20-tooth pulleys (KSC Direct / SDP, RatRig); other rows are the rule, not a maker table
- Page: https://xemstudio.com/objects/gt3-timing-pulleys-3mm-pitch/ · JSON: https://xemstudio.com/api/geometry?object=gt3-timing-pulleys-3mm-pitch · Plain text: https://xemstudio.com/objects/gt3-timing-pulleys-3mm-pitch/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files CC BY 4.0 or their publisher's license
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**Exact dimensions.** True size, with no tolerance added.

## Notes

- GT3 / 3GT (3 mm pitch, also sold as GT2-3M): PD = teeth x 3 / pi. OD = PD − 0.762 mm, i.e. a pitch-line differential of 0.381 mm. That rule rests on two 20-tooth pulleys from two sellers: SDP/SI part 20-3P06M6FA6 via KSC prints PD 19.1 / OD 18.3 (flange Ø22.7, 6 mm belt, 6 mm bore) and RatRig's 9 mm pulley prints PD 0.752 in / OD 0.722 in (19.10 / 18.34 mm; hub 0.5 in, overall width 0.813 in, 1/4 in bore). No GT3 table of other tooth counts was readable, so the other rows apply the rule and are not maker values.
- Belt moves 3 mm per tooth: a 20T pulley moves 60 mm per turn (on a 200-step motor at 16x microstepping that is 3200 / 60 = 53.3 microsteps per mm).
- Sellers list 3 mm pulleys as 'for GT2 or GT3 belts' (KSC) and as 3GT / GT2-3M (RatRig); check the profile printed on the pulley you buy.
- No files: the GT3 tooth form is not published in any source read, and a made-up groove would not mesh.

## Sizes

| teeth | pitch Ø PD, mm | outside Ø OD (PD − 0.762), mm | belt travel per turn, mm |
|---|---|---|---|
| 16 | 15.28 | 14.52 | 48 |
| 18 | 17.19 | 16.43 | 54 |
| 20 | 19.10 | 18.34 | 60 |
| 22 | 21.01 | 20.25 | 66 |
| 24 | 22.92 | 22.16 | 72 |
| 28 | 26.74 | 25.98 | 84 |
| 30 | 28.65 | 27.89 | 90 |
| 32 | 30.56 | 29.80 | 96 |
| 36 | 34.38 | 33.62 | 108 |
| 40 | 38.20 | 37.44 | 120 |
| 44 | 42.02 | 41.25 | 132 |
| 48 | 45.84 | 45.07 | 144 |
| 60 | 57.30 | 56.53 | 180 |
| 72 | 68.75 | 67.99 | 216 |
| 80 | 76.39 | 75.63 | 240 |

## Where the files are

- KSC Direct (SDP/SI part 20-3P06M6FA6): [3 mm pitch 20-tooth timing pulley, 6 mm belt, 6 mm bore: PD 19.1, OD 18.3, flange 22.7](https://kscdirect.com/itemDetail/7281045/20-3p06m6fa6-timing-pulley-aluminum-clear-anodized) — web — Publisher's page; dimensions are facts
- RatRig: [3GT (GT2-3M) 20-tooth pulley, 9 mm belt, 1/4 in bore: PD 0.752 in, OD 0.722 in, hub 0.5 in, overall 0.813 in](https://ratrig.com/products/timing-pulley-3gt-gt2-3m-20-tooth-9mm-belt-25-bore) — web — Publisher's page; dimensions are facts
- Pfeifer Industries: [Timing belt pulley PD / OD charts: PD = pitch x teeth / pi, OD = PD - 2 U (U = cord to tooth root)](https://www.pfeiferindustries.com/information.php?info_id=12) — web — Publisher's page; dimensions are facts

## Questions

**What is the outside diameter of a 20 tooth GT3 pulley?**

18.34 mm: pitch diameter 19.10 mm minus 0.762 mm.

**How far does a GT3 belt move per tooth?**

3 mm; a 20T pulley moves the belt 60 mm per revolution.

**Is GT3 the same as 3GT?**

Sellers use 3GT, GT3 and GT2-3M for the same 3 mm profile; the numbers above are for it.

## 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/)
- [Timing belt profiles: GT2, HTD 3M / 5M / 8M, T5, T10, AT5, MXL, XL, L, H: pitch, tooth height and pulley pitch diameter](https://xemstudio.com/objects/timing-belt-profiles-pitch-and-tooth/)
- [HTD 3M and 5M timing belts: standard lengths (105-3M to 1926-3M, 120-5M to 2350-5M) and tooth counts](https://xemstudio.com/objects/htd-3m-5m-belt-lengths/)