# Tri-clamp cups: closed-end spools (ferrule on a capped tube), 1.5, 2 and 3 in

> What are the dimensions of a 2 inch tri-clamp spool with one end welded shut?

- Category: Stirling engines › Tri-clamp engine parts
- Kind: Hardware
- Basis: ISO 2852 ferrule face (C2/C3, 2.85 mm rim, 1.6 mm recess, 20° back) and 16 ga ASME BPE tube from the tri-clamp ferrule entry; 3 mm flat end plate standing in for a welded cap
- Page: https://xemstudio.com/objects/tri-clamp-cups/ · JSON: https://xemstudio.com/api/geometry?object=tri-clamp-cups · Plain text: https://xemstudio.com/objects/tri-clamp-cups/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

## Notes

- A cup is a spool with one ferrule and the other end closed: in stainless it is a tube with a cap welded on (or a 'tri-clamp end cap spool', sold as such); here it is one printed part. The ferrule end takes a stock clamp and gasket against any head on this shelf.
- What it is for: the hot end of a beta or gamma engine (the cup is the displacer cylinder, the open ferrule end gets the cold head with the rod guide), an alpha cylinder with the piston in it and the head carrying the con-rod gland, a cold-side water jacket cap, or a mock-up to check lengths before buying steel.
- Printed cups are cold-side and mock-up parts: PETG is good to ~70 °C. For a burner-fired hot end buy a stainless capped spool and use the printed one to set the length. Inner diameter matches the steel (34.8 / 47.5 / 72.9), so the displacers and pistons on this shelf fit both.
- Print closed end down, 0.2 mm layers, 3+ walls; the ferrule's 20° back cone needs no supports. Sand the face flat on a sheet of 400 grit on glass so the gasket seals.
- Lengths: 1.5 in 50/75/100, 2 in 60/90/120/150, 3 in 80/120/160; the -rod3 version has a Ø3.2 centre hole in the end for a displacer rod gland on the closed end (beta engines with the drive on the hot side are rare; it is there for a cold-end cup).

## Sizes

| size | od_mm | id_mm | length_mm | end_plate_mm | end |
|---|---|---|---|---|---|
| 1.5 | 38.1 | 34.8 | 50 | 3.0 | plain |
| 1.5 | 38.1 | 34.8 | 75 | 3.0 | plain |
| 1.5 | 38.1 | 34.8 | 100 | 3.0 | plain |
| 1.5 | 38.1 | 34.8 | 75 | 3.0 | Ø3.2 centre hole |
| 2 | 50.8 | 47.5 | 60 | 3.0 | plain |
| 2 | 50.8 | 47.5 | 90 | 3.0 | plain |
| 2 | 50.8 | 47.5 | 120 | 3.0 | plain |
| 2 | 50.8 | 47.5 | 150 | 3.0 | plain |
| 2 | 50.8 | 47.5 | 90 | 3.0 | Ø3.2 centre hole |
| 3 | 76.2 | 72.9 | 80 | 3.0 | plain |
| 3 | 76.2 | 72.9 | 120 | 3.0 | plain |
| 3 | 76.2 | 72.9 | 160 | 3.0 | plain |
| 3 | 76.2 | 72.9 | 120 | 3.0 | Ø3.2 centre hole |

## Where the files are

- ISO: [ISO 2852:1993 Stainless steel clamp pipe couplings for the food industry](https://www.iso.org/standard/7873.html) — standard — ISO (verify at link)
- Long Earth Society: [Tri-clamp Stirling engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (13 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/tri-clamp-cups/index.json

- cup-1.5in-50: [STEP](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-1.5in-50.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-1.5in-50.stl) — 1.5 in closed-end spool Ø38.1 × 50: ISO 2852 ferrule face, 16 ga wall, 3 mm closed end with a 1.5 mm outer fillet (the weld); print closed end down
- cup-1.5in-75: [STEP](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-1.5in-75.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-1.5in-75.stl) — 1.5 in closed-end spool Ø38.1 × 75: ISO 2852 ferrule face, 16 ga wall, 3 mm closed end with a 1.5 mm outer fillet (the weld); print closed end down
- cup-1.5in-100: [STEP](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-1.5in-100.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-1.5in-100.stl) — 1.5 in closed-end spool Ø38.1 × 100: ISO 2852 ferrule face, 16 ga wall, 3 mm closed end with a 1.5 mm outer fillet (the weld); print closed end down
- cup-1.5in-75-rod3: [STEP](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-1.5in-75-rod3.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-1.5in-75-rod3.stl) — 1.5 in closed-end spool × 75 with a Ø3.2 centre hole in the end for a displacer rod or gland
- cup-2in-60: [STEP](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-2in-60.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-2in-60.stl) — 2 in closed-end spool Ø50.8 × 60: ISO 2852 ferrule face, 16 ga wall, 3 mm closed end with a 1.5 mm outer fillet (the weld); print closed end down
- cup-2in-90: [STEP](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-2in-90.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-2in-90.stl) — 2 in closed-end spool Ø50.8 × 90: ISO 2852 ferrule face, 16 ga wall, 3 mm closed end with a 1.5 mm outer fillet (the weld); print closed end down
- cup-2in-120: [STEP](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-2in-120.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-2in-120.stl) — 2 in closed-end spool Ø50.8 × 120: ISO 2852 ferrule face, 16 ga wall, 3 mm closed end with a 1.5 mm outer fillet (the weld); print closed end down
- cup-2in-150: [STEP](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-2in-150.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-2in-150.stl) — 2 in closed-end spool Ø50.8 × 150: ISO 2852 ferrule face, 16 ga wall, 3 mm closed end with a 1.5 mm outer fillet (the weld); print closed end down
- cup-2in-90-rod3: [STEP](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-2in-90-rod3.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-2in-90-rod3.stl) — 2 in closed-end spool × 90 with a Ø3.2 centre hole in the end for a displacer rod or gland
- cup-3in-80: [STEP](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-3in-80.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-3in-80.stl) — 3 in closed-end spool Ø76.2 × 80: ISO 2852 ferrule face, 16 ga wall, 3 mm closed end with a 1.5 mm outer fillet (the weld); print closed end down
- cup-3in-120: [STEP](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-3in-120.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-3in-120.stl) — 3 in closed-end spool Ø76.2 × 120: ISO 2852 ferrule face, 16 ga wall, 3 mm closed end with a 1.5 mm outer fillet (the weld); print closed end down
- cup-3in-160: [STEP](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-3in-160.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-3in-160.stl) — 3 in closed-end spool Ø76.2 × 160: ISO 2852 ferrule face, 16 ga wall, 3 mm closed end with a 1.5 mm outer fillet (the weld); print closed end down
- cup-3in-120-rod3: [STEP](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-3in-120-rod3.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-cups/cup-3in-120-rod3.stl) — 3 in closed-end spool × 120 with a Ø3.2 centre hole in the end for a displacer rod or gland

## How it fits

### Parts that fit it
- [Spool hanger collars: clamp a tri-clamp spool to 2020 extrusion over the flame (1.5, 2, 3 in)](https://xemstudio.com/objects/spool-hanger-collars/): same tube OD

### Connects to
- [Tri-clamp clamps (printable two-bolt), hot-joint gaskets and heat shields: 1.5, 2 and 3 in](https://xemstudio.com/objects/tri-clamp-clamps/): clamps its ferrule face to any head

### Alternatives
- [Tri-clamp spool (two ferrules on a tube), 1.5 and 2 inch](https://xemstudio.com/objects/tri-clamp-spool/): spool + flat end cap
- [Tri-clamp end cap and gasket, 1.5 and 2 inch](https://xemstudio.com/objects/tri-clamp-end-cap/): cap a plain spool

### Also needed
- [Tri-clamp displacers and engine heads: 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-displacers-and-heads/): displacer and cold head
- [Tri-clamp power pistons and crank linkage: full-bore ring-less pistons, con-rods, crank webs and a clamp-on crank frame for 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-power-pistons/): alpha cylinder piston

## Questions

**Can I use a printed tri-clamp cup as the hot end of a Stirling engine?**

Only on a hot-plate or warm-water engine (under ~70 °C for PETG). For a tea light or burner use a stainless capped spool; print the cup to set the length and test the fit first.

**What is the inside diameter of a 2 inch tri-clamp cup?**

47.5 mm, the same as a 16 ga 2 in spool, so the Ø46 displacer and the Ø47.3 lapped piston both fit.

**How do I print the ferrule face so it seals?**

Face up, closed end on the bed; afterwards rub the face on 400 grit on glass until it is uniformly matte, then clamp with a stock gasket.

## Fits with

- [Tri-clamp spool (two ferrules on a tube), 1.5 and 2 inch](https://xemstudio.com/objects/tri-clamp-spool/)
- [Tri-clamp (Tri-Clover) sanitary ferrule, 1/2 to 4 inch](https://xemstudio.com/objects/tri-clamp-ferrule/)
- [Tri-clamp end cap and gasket, 1.5 and 2 inch](https://xemstudio.com/objects/tri-clamp-end-cap/)
- [Tri-clamp displacers and engine heads: 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-displacers-and-heads/)
- [Tri-clamp power pistons and crank linkage: full-bore ring-less pistons, con-rods, crank webs and a clamp-on crank frame for 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-power-pistons/)
- [Tri-clamp clamps (printable two-bolt), hot-joint gaskets and heat shields: 1.5, 2 and 3 in](https://xemstudio.com/objects/tri-clamp-clamps/)