Crane strap brake: steel strap round a drum, tightened by a lever — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/crane-strap-brake-mechanism/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Xem Studio design following Brown No. 242 (1868)
Catalog version: 2026-10-20

Sizes: see table below
- A steel strap wraps most of the way round a drum on the hoist shaft. One end is anchored on the lever's fulcrum, the other on the lever close to it, so pressing the handle pulls the strap tight round the drum. Its grip grows along the wrap: the tension ratio between the ends is e^(μθ), 3.31 for μ = 0.3 over the 228.78° drawn, and the brake torque is (T1 − T2) × R.
- Drum Ø60 × 20, strap 20 × 1.5 touching the drum over 228.78° with both legs tangent, pins 24 mm apart 48 mm below the axis, lever handle 142 mm from the fulcrum. Drawn snug, lever level.
- Brown's No. 242 (strap brake used on cranes).
- Parts (each has its own page): brake-drum-60x20-bore10, brake-strap-20x1-5-drum60-pins24, strap-brake-lever-130-pins24, dowel-pins-metric, linear-shafts-h6.
- Brown's movement No. 242 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.

parameter  value
drum  Ø60
wrap  228.78°
tension ratio (μ 0.3)  3.31
lever ratio  ≈ 6 : 1

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. 242: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_242.html

Free files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/crane-strap-brake-mechanism/index.json
API: https://xemstudio.com/api/geometry?object=crane-strap-brake-mechanism