Spur gears, involute 20°: module 0.5, 1 and 2, 12–60 teeth — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/spur-gears-involute/  (CC BY 4.0)
Basis: ISO 53 / DIN 867 basic rack, 20° pressure angle, standard addendum (1 m) and dedendum (1.25 m); true involute flanks generated point by point
Catalog version: 2026-10-20

Sizes: see table below
- Pitch diameter = module × teeth; outer diameter = module × (teeth + 2); centre distance between two gears = module × (N1 + N2) / 2. Module 1, 20T + 40T → 30 mm centres.
- Printed gears: module 1 is the practical floor on an FDM printer with a 0.4 mm nozzle; module 0.5 needs resin. Add 0.1–0.15 mm to the centre distance for backlash on printed pairs.
- Bores are plain; hubs carry an M3 set-screw hole. Pair with the 623/625 bearings and 3/5 mm dowels in the library for a crank train.
- Long Earth Society: gear trains for Stirling displacer drives and the 2:1 reduction on the flywheel-driven generator builds.

module  teeth  pitch_dia_mm  outer_dia_mm  root_dia_mm  face_mm  bore_mm
1  12  12.0  14.0  9.5  6  3
1  15  15.0  17.0  12.5  6  3
1  16  16.0  18.0  13.5  6  4
1  20  20.0  22.0  17.5  6  5
1  24  24.0  26.0  21.5  6  5
1  30  30.0  32.0  27.5  6  5
1  36  36.0  38.0  33.5  6  6
1  40  40.0  42.0  37.5  6  6
1  48  48.0  50.0  45.5  6  8
1  60  60.0  62.0  57.5  6  8
0.5  16  8.0  9.0  6.75  4  2
0.5  20  10.0  11.0  8.75  4  2
0.5  24  12.0  13.0  10.75  4  3
0.5  30  15.0  16.0  13.75  4  3
0.5  40  20.0  21.0  18.75  4  3
0.5  60  30.0  31.0  28.75  4  4
2  12  24.0  28.0  19.0  10  5
2  15  30.0  34.0  25.0  10  6
2  20  40.0  44.0  35.0  10  8
2  30  60.0  64.0  55.0  10  8
2  40  80.0  84.0  75.0  10  10

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Wikipedia: Involute gear — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Involute_gear
- Wikipedia: Gear — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Gear
- KHK Gears: Gear technical reference (module, pressure angle, formulas) — web, PDF — KHK site terms [verify license at link] — https://khkgears.net/new/gear_knowledge/
- Long Earth Society: Engine builds that use these parts (videos and write-ups) — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 21 parts): https://xemstudio.com/files/hardware/spur-gears-involute/index.json
API: https://xemstudio.com/api/geometry?object=spur-gears-involute