Eccentric and strap: Ø30 eccentrics at 3, 5 and 8 mm offset with a split strap — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/eccentric-and-strap/  (CC BY 4.0)
Basis: Eccentric sheave: a disc on a shaft offset e from its centre gives a stroke of 2e; strap fits the Ø30 disc exactly
Catalog version: 2026-10-20

Sizes: see table below
- A disc mounted off-centre on the shaft turns inside a strap; the strap's arm moves back and forth with a stroke of twice the offset.
- Three discs: 3, 5 and 8 mm offset for 6, 10 and 16 mm stroke. All take a Ø5 shaft and have a Ø2.5 set-screw hole.
- The strap is split so it goes over the disc without taking the shaft apart; its 40 mm arm ends in a Ø3 eye 51 mm from the strap's centre.
- The load is spread round the whole strap, so it runs quietly; the usual way to drive a pump or a valve.

offset e  stroke  disc  shaft
3 mm  6 mm  Ø30 × 8  Ø5
5 mm  10 mm  Ø30 × 8  Ø5
8 mm  16 mm  Ø30 × 8  Ø5

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Wikipedia: Eccentric (mechanism) — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Eccentric_(mechanism)
- Long Earth Society: Engine and rig builds on extrusion frames — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 4 parts): https://xemstudio.com/files/hardware/eccentric-and-strap/index.json
API: https://xemstudio.com/api/geometry?object=eccentric-and-strap