Flexure hub collars: split collars Ø13.2, Ø17.6 and Ø22 for Ø3 rod and Ø5 tube — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/flexure-hub-collar/  (CC BY 4.0)
Basis: Collar Ø = flexure hub Ø (max(bore + 8, 0.22 × OD)); 6 mm thick so the M3 pinch screw's head (Ø5.5) stays within it; 0.8 mm slit; M3 pinch (Ø2.5)
Catalog version: 2026-10-20

Sizes: see table below
- A split clamping collar the size of a flexure leaf's hub: two per stack, one each end, squeeze the leaves, hub washers and spacers onto the rod.
- Ø13.2 (for Ø60 leaves), Ø17.6 (Ø80) and Ø22 (Ø100), all 6 mm thick. b5 collars have a Ø5 bore for the 5 mm tube piston rod; b3 collars a Ø3 bore for the displacer rod.
- A 0.8 mm slit runs from the bore to the rim, closed by an M3 × 10 screw in a Ø2.5 tangential hole at mid-thickness; the screw head stays inside the collar's 6 mm, clear of the leaf beside it.

flexure_od_mm  collar_od_mm  bore_mm  thickness_mm  slit_mm  pinch
60  13.2  5 / 3  6  0.8  M3 (Ø2.5)
80  17.6  5 / 3  6  0.8  M3 (Ø2.5)
100  22.0  5 / 3  6  0.8  M3 (Ø2.5)

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, 6 parts): https://xemstudio.com/files/hardware/flexure-hub-collar/index.json
API: https://xemstudio.com/api/geometry?object=flexure-hub-collar