GT3 (3GT, 3 mm pitch) timing pulleys: pitch diameter and outside diameter, 16T to 80T — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/gt3-timing-pulleys-3mm-pitch/  (sheet CC BY 4.0)
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
Catalog version: 2026-10-20

Sizes: see table below
- 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.

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

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- 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 — web — Publisher's page; dimensions are facts — https://kscdirect.com/itemDetail/7281045/20-3p06m6fa6-timing-pulley-aluminum-clear-anodized
- 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 — web — Publisher's page; dimensions are facts — https://ratrig.com/products/timing-pulley-3gt-gt2-3m-20-tooth-9mm-belt-25-bore
- Pfeifer Industries: Timing belt pulley PD / OD charts: PD = pitch x teeth / pi, OD = PD - 2 U (U = cord to tooth root) — web — Publisher's page; dimensions are facts — https://www.pfeiferindustries.com/information.php?info_id=12

No true-size file yet: the published figures do not fix the whole shape; a measured scan is planned.
API: https://xemstudio.com/api/geometry?object=gt3-timing-pulleys-3mm-pitch