Double-helical (herringbone) gear, normal module 1.5, 30 teeth, helix 20° , face 16, Ø8 bore — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/double-helical-gear-mn1-5-30t-beta20-bore8/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Xem Studio design following Brown's figure (1868); true size, no printing allowance
Catalog version: 2026-10-20

Overall (mm): length 50.89, width 50.89, height 16.0
- Normal module 1.5, helix angle 20°: transverse module 1.6, transverse pressure angle 21.17°, pitch Ø47.89, tip Ø50.89, root Ø44.14; addendum 1.5, dedendum 1.88 (normal-module depths).
- Two opposed 20° helices meet at mid-face (twist 6.97° each way over 8 mm), so the end thrusts cancel.
- Xem Studio design following Brown's figure; true size, no printing allowance (apply your own to the mating features).

dimension  value
normal module  1.5
teeth  30
helix angle  20°
transverse module  1.6
pitch Ø  47.89 mm
tip Ø  50.89 mm
face  16 mm
bore  Ø8

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Henry T. Brown (1868, public domain): Five Hundred and Seven Mechanical Movements — scan on archive.org — web — Publisher's page; dimensions are facts — https://archive.org/details/fivehundredseven00browiala
- 507movements.com: Brown's movement No. 41: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_041.html
- Xem Studio: drawing — web — Publisher's page; dimensions are facts — https://xemstudio.com/objects/double-helical-gears-mechanism/

Free files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/double-helical-gear-mn1-5-30t-beta20-bore8/index.json
API: https://xemstudio.com/api/geometry?object=double-helical-gear-mn1-5-30t-beta20-bore8