Power piston Ø16, 20, 25, 30 with Ø3 wrist-pin boss — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/power-piston/  (CC BY 4.0)
Basis: Piston OD = liner bore (fit: run), length 0.9 × bore; Ø3 rod hole and Ø3 wrist-pin hole
Catalog version: 2026-10-20

Sizes: see table below
- The piston for the flanged liners, drawn at the liner bore exactly: Ø16 × 14, Ø20 × 18, Ø25 × 22, Ø30 × 27, with a 0.5 chamfer at the crown.
- Hollow with 2 mm walls; its closed end has a Ø3 hole (fit: slide) for a Ø3 piston rod.
- Inside the -blank piston, a wrist-pin bar across the bore carries a Ø3 hole (fit: press) at 0.4 × length + 4 from the closed end.
- Two kinds per bore: the -blank piston has a Ø3 rod hole in its crown and a solid wrist-pin bar (for a crosshead and piston rod); the -trunk piston has a closed 2 mm crown and two wrist-pin bosses 7 mm apart, so a 5 mm con-rod's small end (R7 eye) goes straight on its Ø3 wrist pin with 1 mm each side.

file  diameter  length  rod hole  wrist-pin hole
piston-16x14-blank  16  14  3  3
piston-20x18-blank  20  18  3  3
piston-25x22-blank  25  22  3  3
piston-30x27-blank  30  27  3  3

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Wikipedia: Crosshead — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Crosshead
- Wikipedia: Piston — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Piston
- James R. Senft: Miniature Stirling engine piston fits (LTD book) — book — reference [verify license at link] — https://www.stirlingengine.com/
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 8 parts): https://xemstudio.com/files/hardware/power-piston/index.json
API: https://xemstudio.com/api/geometry?object=power-piston