LEARN · 2026-10-06
GT2 timing pulley guide: tooth count, belt width, flanges and centre distance
How to compute GT2 (2GT) pulley pitch and outside diameters, choose tooth count, belt width and flanges, and size the centre distance and steps/mm.
What is GT2?
GT2 (2GT) is a 2 mm-pitch curvilinear-tooth timing belt with low backlash and smooth engagement — the standard drive of 3D printers, laser cutters and small CNC machines. Common widths are 6 and 9 mm; closed loops come in 200, 280, 400, 610 mm and more.
Pitch diameter PD = teeth × 2 / π OD = PD − 0.508 mm
Common tooth counts
| Teeth | PD (mm) | OD (mm) | Travel / rev (mm) |
|---|---|---|---|
| 16 | 10.19 | 9.68 | 32 |
| 20 | 12.73 | 12.22 | 40 |
| 30 | 19.10 | 18.59 | 60 |
| 36 | 22.92 | 22.41 | 72 |
| 40 | 25.46 | 24.96 | 80 |
| 60 | 38.20 | 37.69 | 120 |
Choosing teeth and flanges
- 20 teeth (40 mm per revolution) is the 3D-printer XY classic; 16 teeth gives more resolution but less wrap and belt life.
- Keep at least 6 teeth in mesh, or the belt can skip.
- Drive pulleys usually have two flanges; idlers can be flanged smooth bearings or toothed.
- A 5 mm bore fits NEMA17 steppers — use a D-cut or set screw.
Belt length and centre distance
L ≈ 2C + π(D₁ + D₂)/2 + (D₁ − D₂)² / (4C)
C is the centre distance and D the pitch diameters. Closed belts come in 2 mm multiples, so pick a standard length and solve for C — the GT2 centre-distance calculator does it and opens the matching pulleys.
FAQ
steps/mm for a GT2 20-tooth pulley?
With a 1.8° stepper at 16 microsteps: 3200 ÷ 40 = 80 steps/mm.
Can GT2 pulleys be 3D printed?
Yes — PETG or nylon at 0.2 mm layers works, but tooth accuracy limits positioning; SLS / MJF is better for precision.
Can GT2 mix with T2.5 or MXL?
No — pitch and tooth shape differ. GT2 pulleys need GT2 belts.