Tri-clamp displacers and engine heads: 1.5, 2 and 3 in spools — dimension sheet Source: Xem Studio, https://xemstudio.com/objects/tri-clamp-displacers-and-heads/ (CC BY 4.0) Basis: 16 ga ASME BPE tube bores (1.5 in = 34.8 mm, 2 in = 47.5, 3 in = 72.9) from the tri-clamp spool entry; displacer radial gap 0.6–1.0 mm for low-ΔT air engines (Senft); ISO 2852 cap face from the tri-clamp end cap entry Catalog version: 2026-10-20 Sizes: see table below - Displacer diameter = bore − 2 × gap: 1.5 in → Ø33.6, 2 in → Ø46.0, 3 in → Ø70.9. Length 1.5–2.5 × bore (the longer, the bigger the temperature difference it can hold across itself); stroke 0.3–0.4 × length. A 2 in × 6 in spool takes the Ø46 × 90 displacer with a 30 mm stroke. - Shell displacers: 1 mm wall, closed hot end, internal rings every 25 mm, printed open end up (no supports); the cap presses in and carries the Ø3 rod on an M3 grub. Mass matters less than you think at 2–5 Hz; stiffness and straightness matter more. PETG for a cold end under 80 °C; the hot end of the displacer sees the hot plate only by radiation: PETG survives a tea-light engine, use a foam-and-foil or a thin stainless cup over the nose for a burner engine. - Regenerative (annular-gap) displacer: 1.5 mm gap and 12 slots packed with #100 stainless mesh turn the gap into the regenerator (Senft's LTD trick); use it in a single spool with no separate regenerator section. Foam templates: cut closed-cell foam (EVA, pool noodle) to Ø and length with the cross lines for centring the rod. - Heads (ISO 2852 caps with features on the back, so a stock clamp and gasket seal them): displacer head (3/32 in brass guide tube press-fit on centre + 4 mm barb), power head (10 mL syringe barrel socket, Ø15.9, as the power cylinder + M5 port), instrument head (DS18B20, K-type and a barb), crank head (Ø3 rod gland with an O-ring groove and two 623 towers 24 mm up for a crankshaft right on the cap). Heads print flat, face down, at 0.15 mm layers; sand the sealing land. - Engine recipes: Gamma, 2 in: hot ferrule + 6 in spool + displacer head on top, Ø46 × 90 shell displacer, power head with a 10 mL syringe on a side tee or the crank head; flywheel Ø100 on the crank kit. Beta: one spool, regenerative displacer, crank head on the cold end. Free-piston: 2 in spool, Ø46 displacer on the spiral flexures, power piston from the free-piston core. - LES: this is the shelf the LES engines are literally built from; every head here replaces a flat cap that used to be drilled by hand. spool bore_mm displacer_od_mm length_mm radial_gap_mm type 1.5 34.800000000000004 33.6 50 0.6 shell / foam 1.5 34.800000000000004 33.6 75 0.6 shell / foam 1.5 34.800000000000004 33.6 100 0.6 shell / foam 2 47.5 46.0 60 0.75 shell / foam 2 47.5 46.0 90 0.75 shell / foam 2 47.5 46.0 120 0.75 shell / foam 3 72.9 70.9 80 1.0 shell / foam 3 72.9 70.9 120 1.0 shell / foam 3 72.9 70.9 160 1.0 shell / foam 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, 46 parts): https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/index.json API: https://xemstudio.com/api/geometry?object=tri-clamp-displacers-and-heads