Tri-clamp flexure head: ISO 2852 cap with Ø60, Ø80 and Ø100 flexure seats — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/tri-clamp-flexure-head/  (CC BY 4.0)
Basis: ISO 2852 cap face; pedestal Ø = tube OD; plate Ø = flexure OD + 16 with a flexure-OD × 1 seat and 3 × Ø3.4 on the flexure rim-hole circle (0.88 × OD)
Catalog version: 2026-10-20

Sizes: see table below
- The head of the tri-clamp free-piston engine: it clamps on the spool's open ferrule and carries the piston's flexure stack (stack A).
- Base: 6 mm ISO 2852 cap, pedestal the tube's OD (38.1 / 50.8 / 76.2) to 14 mm so the clamp clears, then a plate 4 mm thick, Ø76 / Ø96 / Ø116. Overall 18 mm.
- On top: a seat Ø60 / Ø80 / Ø100 × 1 mm deep (the flexure OD) and three Ø3.4 holes on the flexure's rim-hole circle (Ø52.8 / Ø70.4 / Ø88). A centre window Ø19.2 / Ø23.6 / Ø28 (hub + 6) lets the rods through.

spool_in  flange_od_mm  plate_od_mm  flexure_seat_mm  rim_hole_circle_mm  window_mm  height_mm
1.5  50.5  76  Ø60 × 1  52.8  19.2  18
2  64.0  96  Ø80 × 1  70.4  23.6  18
3  91.0  116  Ø100 × 1  88.0  28.0  18

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- NASA NTRS: Free-piston Stirling convertor flexure bearing development and life testing — pdf — US Government work — https://ntrs.nasa.gov/citations/20050182933
- Long Earth Society: Tri-clamp Stirling engine builds — web, video — LES site — https://longearthsociety.com/engineering/
- Wikipedia: Free-piston engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Free-piston_engine

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