Tri-clamp displacer: Ø33.6, Ø46 and Ø70.9 for 1.5, 2 and 3 in spools — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/tri-clamp-displacer/  (CC BY 4.0)
Basis: 16 ga ASME BPE tube bores (1.5 in 34.8, 2 in 47.5, 3 in 72.9 mm) minus a designed radial gap of 0.6 / 0.75 / 1.0 mm (Senft, low-temperature-difference air engines)
Catalog version: 2026-10-20

Sizes: see table below
- The displacer is a closed cylinder that runs in the spool bore with a designed radial gap: 0.6 mm in the 1.5 in spool (Ø33.6 in Ø34.8), 0.75 mm in the 2 in (Ø46.0 in Ø47.5), 1.0 mm in the 3 in (Ø70.9 in Ø72.9). The gap is part of the design and is drawn as is.
- Lengths: 1.5 in 50 / 75 / 100, 2 in 60 / 90 / 120, 3 in 80 / 120 / 160 mm. Each length comes two ways: a hollow shell (1 mm wall, closed rounded end, 1.2 mm internal rings every 25 mm) with its end cap, and a solid body of the same diameter and length with a Ø3 centre hole and two 0.6 mm slots crossing on the axis through the full length, so the file is four quarter-segments around the centre hole.
- The shell's end cap has a spigot Ø(D − 2) × 3 that enters the shell, a Ø D × 1.5 flange, and a Ø16 × 6 boss with the Ø3 rod hole and a Ø2.5 radial hole for an M3 grub at 8 mm; the cap stands 10.5 mm overall. One cap file per spool size serves every length.
- The Ø3 rod is the displacer rod: it leaves through the displacer head or crank head on the cold end. Every hole that meets another part is in the Mating features table.

spool_in  bore_mm  displacer_od_mm  length_mm  radial_gap_mm
1.5  34.8  33.6  50  0.6
1.5  34.8  33.6  75  0.6
1.5  34.8  33.6  100  0.6
2  47.5  46.0  60  0.75
2  47.5  46.0  90  0.75
2  47.5  46.0  120  0.75
3  72.9  70.9  80  1.0
3  72.9  70.9  120  1.0
3  72.9  70.9  160  1.0

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Long Earth Society: Tri-clamp Stirling engine builds — web, video — LES site — https://longearthsociety.com/engineering/
- James R. Senft: An Introduction to Low Temperature Differential Stirling Engines (displacer and gap design) — book — Moriya Press [verify license at link] — https://www.stirlingengine.com/
- Wikipedia: Stirling engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Stirling_engine

Free files (CC BY 4.0, Xem Studio; STEP + STL, 27 parts): https://xemstudio.com/files/hardware/tri-clamp-displacer/index.json
API: https://xemstudio.com/api/geometry?object=tri-clamp-displacer