Clearance-seal pistons Ø48.00 × 34 for a bored 2 in spool: rod (gamma) and gland (beta) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/stirling-clearance-seal-pistons/  (CC BY 4.0)
Basis: Design values; leakage from plane Poiseuille flow in the clearance (Hagen–Poiseuille)
Catalog version: 2026-10-20

Sizes: see table below
- Ø48.00 × 34, no rings: the ground OD in the honed Ø48.00 bore is the seal. It is driven through a rod and a crosshead guided outside the cylinder, so it carries no side load and keeps its clearance.
- Gamma piston: the Ø8 rod screws into the boss and is locked with an M8 nut on the boss end.
- Beta piston: the displacer rod passes through a 6 × 10 × 10 sleeve bushing at the crown (its gland), and the hollow Ø10 piston rod screws into the boss until it bottoms.
- Leakage loss in the cycle model (charged air, 600 rpm): 0.44 / 1.50 / 3.54 W at 10 / 15 / 20 µm radial clearance on the gamma.

part  od_mm  length_mm  rod
piston-48-gamma-m8  48.0  34.0  M8 socket
piston-48-beta-gland  48.0  34.0  gland + M10 × 1 socket

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Wikipedia: Hagen–Poiseuille equation: annular clearance leakage Q = π D δ³ Δp / 12 μ L — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Hagen%E2%80%93Poiseuille_equation
- 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/stirling-clearance-seal-pistons/index.json
API: https://xemstudio.com/api/geometry?object=stirling-clearance-seal-pistons