# Silicone and PU tube, hose barbs and push-fit fittings (the transfer port) > What size silicone tube and barb for a Stirling engine transfer port? - Category: Hardware › Pipe & fittings - Kind: Hardware - 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 - Page: https://xemstudio.com/objects/silicone-tube-and-fittings/ · JSON: https://xemstudio.com/api/geometry?object=silicone-tube-and-fittings · Plain text: https://xemstudio.com/objects/silicone-tube-and-fittings/sheet.txt - License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses ## Notes - 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. ## Sizes | 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 | ## Where the files are - Wikipedia: [Hose barb](https://en.wikipedia.org/wiki/Hose_barb) — web — CC BY-SA 4.0 (text) - Wikipedia: [Push-fit fitting](https://en.wikipedia.org/wiki/Push-to-connect_fitting) — web — CC BY-SA 4.0 (text) - McMaster-Carr: [Tubing (free STEP per part, for your own design use; no redistribution)](https://www.mcmaster.com/products/tubing/) — STEP, PDF — McMaster-Carr site terms (verify at link) - Long Earth Society: [Engine and rig builds](https://longearthsociety.com/engineering/) — web, video — LES site ## Free STEP/STL (22 parts, CC BY 4.0, Xem Studio) Index: https://xemstudio.com/files/hardware/silicone-tube-and-fittings/index.json - silicone-tube-1x3-50: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/silicone-tube-1x3-50.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/silicone-tube-1x3-50.stl) — silicone tube 1 ID × 3 OD, 50 mm - silicone-tube-2x4-50: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/silicone-tube-2x4-50.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/silicone-tube-2x4-50.stl) — silicone tube 2 ID × 4 OD, 50 mm - silicone-tube-3x5-50: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/silicone-tube-3x5-50.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/silicone-tube-3x5-50.stl) — silicone tube 3 ID × 5 OD, 50 mm - silicone-tube-4x6-50: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/silicone-tube-4x6-50.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/silicone-tube-4x6-50.stl) — silicone tube 4 ID × 6 OD, 50 mm - silicone-tube-5x8-50: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/silicone-tube-5x8-50.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/silicone-tube-5x8-50.stl) — silicone tube 5 ID × 8 OD, 50 mm - silicone-tube-6x9-50: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/silicone-tube-6x9-50.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/silicone-tube-6x9-50.stl) — silicone tube 6 ID × 9 OD, 50 mm - silicone-tube-8x12-50: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/silicone-tube-8x12-50.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/silicone-tube-8x12-50.stl) — silicone tube 8 ID × 12 OD, 50 mm - silicone-tube-10x14-50: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/silicone-tube-10x14-50.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/silicone-tube-10x14-50.stl) — silicone tube 10 ID × 14 OD, 50 mm - pu-tube-4x2.5-50: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pu-tube-4x2.5-50.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pu-tube-4x2.5-50.stl) — PU pneumatic tube 4 OD × 2.5 ID, 50 mm - pu-tube-6x4-50: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pu-tube-6x4-50.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pu-tube-6x4-50.stl) — PU pneumatic tube 6 OD × 4 ID, 50 mm - pu-tube-8x5.5-50: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pu-tube-8x5.5-50.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pu-tube-8x5.5-50.stl) — PU pneumatic tube 8 OD × 5.5 ID, 50 mm - pu-tube-10x6.5-50: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pu-tube-10x6.5-50.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pu-tube-10x6.5-50.stl) — PU pneumatic tube 10 OD × 6.5 ID, 50 mm - pu-tube-12x8-50: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pu-tube-12x8-50.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pu-tube-12x8-50.stl) — PU pneumatic tube 12 OD × 8 ID, 50 mm - barb-2mm: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/barb-2mm.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/barb-2mm.stl) — hose barb for 2 mm ID tube, 3 barbs, hex base; print and tap or glue - barb-3mm: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/barb-3mm.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/barb-3mm.stl) — hose barb for 3 mm ID tube, 3 barbs, hex base; print and tap or glue - barb-4mm: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/barb-4mm.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/barb-4mm.stl) — hose barb for 4 mm ID tube, 3 barbs, hex base; print and tap or glue - barb-6mm: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/barb-6mm.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/barb-6mm.stl) — hose barb for 6 mm ID tube, 3 barbs, hex base; print and tap or glue - barb-8mm: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/barb-8mm.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/barb-8mm.stl) — hose barb for 8 mm ID tube, 3 barbs, hex base; print and tap or glue - pushfit-4mm-g1-8: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pushfit-4mm-g1-8.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pushfit-4mm-g1-8.stl) — push-fit fitting envelope: 4 mm tube, G1/8 thread stub - pushfit-6mm-g1-8: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pushfit-6mm-g1-8.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pushfit-6mm-g1-8.stl) — push-fit fitting envelope: 6 mm tube, G1/8 thread stub - pushfit-6mm-g1-4: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pushfit-6mm-g1-4.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pushfit-6mm-g1-4.stl) — push-fit fitting envelope: 6 mm tube, G1/4 thread stub - pushfit-8mm-g1-4: [STEP](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pushfit-8mm-g1-4.step) · [STL](https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pushfit-8mm-g1-4.stl) — push-fit fitting envelope: 8 mm tube, G1/4 thread stub ## Questions **What silicone tube for a Stirling transfer port?** 4 mm ID × 6 mm OD, kept under 30 mm long; the can-cap port is Ø4.2 for a 4 mm barb. **What barb size for 6 mm ID silicone tube?** 7.2 mm barb OD (ID + 1.2), three barbs 2.5 mm long; silicone stretches on and seals without a clamp at low pressure. **What is the ID of 6 mm PU pneumatic tube?** 4 mm (6 × 4); 8 mm tube is 5.5 ID, 4 mm tube is 2.5 ID. ## Fits with - [Pipe thread envelopes: NPT (ANSI B1.20.1) and BSP (ISO 228 / 7), 1/8 to 1 inch](https://xemstudio.com/objects/npt-bsp-thread-envelopes/) - [Can-engine printed kit: can caps, diaphragm clamps, displacer guides, crank stands, CD/platter hubs, syringe cradles](https://xemstudio.com/objects/can-engine-printed-kit/) - [Plastic syringes 1–60 mL as pistons and cylinders](https://xemstudio.com/objects/plastic-syringes/) - [O-rings, common metric sizes (ISO 3601)](https://xemstudio.com/objects/o-rings-metric/) - [Copper pipe (ASTM B88 Type L and M), 1/4 to 2 inch](https://xemstudio.com/objects/copper-pipe-type-l-m/)