Silicone and PU tube, hose barbs and push-fit fittings (the transfer port) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/silicone-tube-and-fittings/  (CC BY 4.0)
Basis: Common silicone tube sizes (ID × OD, 1–2 mm wall), ISO 6432-style PU pneumatic tube (4/6/8/10/12 mm OD), barb geometry (OD = tube ID + 1.2, 3 barbs), push-fit envelopes
Catalog version: 2026-10-20

Sizes: see table below
- Silicone tube ID × OD: 1×3, 2×4, 3×5, 4×6, 5×8, 6×9, 8×12, 10×14 mm; 60 Shore A, −60 to 200 °C, stretches over a barb 1.5 mm larger than its ID. PU pneumatic tube (push-fit): 4×2.5, 6×4, 8×5.5, 10×6.5, 12×8 OD×ID; stiff, rated 10 bar, 80 °C max.
- Transfer port on a can/test-tube Stirling: 4 mm ID silicone, as short as possible (every mL of tube is dead volume that costs compression ratio); the can-cap port is Ø4.2 for a 4 mm barb. Larger engines: 6–8 mm ID.
- Barbs: OD = tube ID + 1.2 mm, three 2.5 mm barbs, a hex base; printed barbs seal silicone tube fine (sand the layer lines). Push-fit fittings take the PU tube OD exactly: 6 mm tube into a 6 mm fitting; thread stubs G1/8 (9.73 OD) or G1/4 (13.16).
- LES: 4 × 6 silicone between the hot and cold spools on the demonstrators; 6 mm PU + push-fits on the pressurised engines.

tube  id_mm  od_mm  wall_mm  barb_od_mm
silicone  1  3  1.0  2.2
silicone  2  4  1.0  3.2
silicone  3  5  1.0  4.2
silicone  4  6  1.0  5.2
silicone  5  8  1.5  6.2
silicone  6  9  1.5  7.2
silicone  8  12  2.0  9.2
silicone  10  14  2.0  11.2
PU push-fit  2.5  4  0.75  push-fit
PU push-fit  4  6  1.0  push-fit
PU push-fit  5.5  8  1.25  push-fit
PU push-fit  6.5  10  1.75  push-fit
PU push-fit  8  12  2.0  push-fit

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Wikipedia: Hose barb — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Hose_barb
- Wikipedia: Push-fit fitting — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Push-to-connect_fitting
- McMaster-Carr: Tubing (free STEP per part, for your own design use; no redistribution) — STEP, PDF — McMaster-Carr site terms [verify license at link] — https://www.mcmaster.com/products/tubing/
- Long Earth Society: Engine and rig builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 22 parts): https://xemstudio.com/files/hardware/silicone-tube-and-fittings/index.json
API: https://xemstudio.com/api/geometry?object=silicone-tube-and-fittings