Thermoacoustic hot-end fin sleeve: radial fins that slide over a 2 in closed-end cup — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/thermoacoustic-hot-fin-sleeve/  (CC BY 4.0)
Basis: ASME BPE 2 in tube OD Ø50.8 (the sleeve's bore); fin count, thickness and reach are design values; M4 set screws ISO 4026
Catalog version: 2026-10-20

Sizes: see table below
- A separate, optional heat exchanger for the closed hot end of the standing-wave engines: a sleeve whose bore is exactly the tube's Ø50.8 slides over the closed end of the plain cup-2in-133.35 (a standard closed-end 2 in spool, 133.35 mm), and 16 radial fins carry the torch's heat into the hot cavity and the hot exchanger. Three M4 set screws in a band above the fins hold it.
- It covers 49 to 131.85 mm from the cup's face, so it stays clear of the water jacket and the clamp; the fins reach Ø80, as far from the tube as the Ø76 fins the hot end used to carry built on.
- Without it the flame heats the bare cup: the engine is complete and still runs, but needs more heat to start. The cup stays a plain part a sanitary fabricator makes; the sleeve can be made any way you like.
- Fits: the bore slides on the tube OD (slide fit), the set screws clamp it.

feature  value
bore  Ø50.8 (tube OD)
length  82.85
wall  2.0
fins  16 × 1.6 thick, to Ø80
set screws  3 × M4, 0 / 120 / 240°
fits  cup-2in-133.35

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- G. W. Swift (LANL / Acoustical Society of America): Thermoacoustics: A Unifying Perspective for Some Engines and Refrigerators (Rott's equations, screen relations, DeltaEC) — web, software — LANL [verify license at link] — https://www.lanl.gov/org/ddste/aldps/materials-physics-applications/condensed-matter-magnet-science/thermoacoustics/
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/thermoacoustic-hot-fin-sleeve/index.json
API: https://xemstudio.com/api/geometry?object=thermoacoustic-hot-fin-sleeve