Tri-clamp crank frame: ISO 2852 cap with 608 towers for a Ø8 crankshaft, 1.5, 2 and 3 in — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/tri-clamp-crank-frame/  (CC BY 4.0)
Basis: ISO 2852 cap face; pedestal Ø = tube OD to clear the clamp; two 8 mm towers with Ø22 608 pockets, 21 mm apart, crank axis 32 / 34 / 40 mm above the face
Catalog version: 2026-10-20

Sizes: see table below
- A crank frame that clamps onto the open ferrule of a spool with a stock clamp and gasket, and holds a Ø8 crankshaft in two 608 bearings above it.
- Base: the 6 mm ISO 2852 cap, a pedestal the tube's OD (38.1 / 50.8 / 76.2) up to 14 mm so the clamp clears, and a Ø C3 plate 4 mm thick on top. A con-rod window Ø21 / Ø28 / Ø44 runs through the centre.
- Two towers 8 mm thick with rounded tops stand 21 mm apart; each has a Ø22 × 7 pocket for a 608 from the outside face, and the shaft hole between is Ø9.2 so the Ø8 shaft touches only the bearings.
- Crank axis 32 / 34 / 40 mm above the face for 1.5 / 2 / 3 in; overall height 47.7 / 54 / 60 mm.

spool_in  flange_od_mm  window_mm  crank_axis_mm  tower_gap_mm  bearing  overall_h_mm
1.5  50.5  21  32  21  608 (Ø22)  47.7
2  64.0  28  34  21  608 (Ø22)  54.0
3  91.0  44  40  21  608 (Ø22)  60.0

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Long Earth Society: Tri-clamp Stirling engine builds — web, video — LES site — https://longearthsociety.com/engineering/
- James R. Senft: An Introduction to Stirling Engines (piston fit and leakage) — book — Moriya Press [verify license at link] — https://www.stirlingengine.com/
- ASME: BPE tube dimensions (16 ga sanitary tube) — standard — ASME [verify license at link] — https://www.asme.org/codes-standards/find-codes-standards/bpe-bioprocessing-equipment

Free files (CC BY 4.0, Xem Studio; STEP + STL, 3 parts): https://xemstudio.com/files/hardware/tri-clamp-crank-frame/index.json
API: https://xemstudio.com/api/geometry?object=tri-clamp-crank-frame