Linear alternator cap ring, Ø96 and Ø116 — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/linear-alternator-cap-ring/  (CC BY 4.0)
Basis: Same outline and rim circle as the housing's top flange; bore = sleeve bore − 2
Catalog version: 2026-10-20

Sizes: see table below
- A flat ring Ø96 (2 in) or Ø116 (3 in) × 4 with a Ø50.5 bore, that holds the back-iron sleeve and bobbin down in the housing.
- 3 × Ø3.4 holes on the same rim circle as the housing (R35.2 / R44): M3 × 12 screws go up through the top flange and cap into the standoffs that carry the flexure ring and stack B.

file  outside  bore  thickness  rim circle
alt-cap-2in-flex80  96  50.5  4  R35.2
alt-cap-3in-flex100  116  50.5  4  R44

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- NASA (NTRS, public domain): Linear alternator design for free-piston Stirling convertors (2005) — PDF — US Government work, public domain — https://ntrs.nasa.gov/search?q=20050182934
- NASA (NTRS, public domain): Sunpower/NASA 80 We free-piston Stirling convertor (2002) — PDF — US Government work, public domain — https://ntrs.nasa.gov/search?q=20020047256
- Wikipedia: Linear alternator — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Linear_alternator
- Wikipedia: Free-piston engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Free-piston_engine
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 2 parts): https://xemstudio.com/files/hardware/linear-alternator-cap-ring/index.json
API: https://xemstudio.com/api/geometry?object=linear-alternator-cap-ring