# Ringbom displacer cap for an 8 mm rod, 2 in shell displacer

> How do I fit a Ringbom rod to a tri-clamp displacer?

- Category: Hardware › Stirling & thermoacoustic
- Kind: Hardware
- Basis: Shell spigot and flange as the displacer cap on this site (2 in shell Ø46 × 1 mm wall); Ø8 rod and M4 grub sizes are design values
- Page: https://xemstudio.com/objects/tri-clamp-ringbom-displacer-cap/ · JSON: https://xemstudio.com/api/geometry?object=tri-clamp-ringbom-displacer-cap · Plain text: https://xemstudio.com/objects/tri-clamp-ringbom-displacer-cap/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** Every file is drawn at true size with no printing tolerance. The holes and pins that meet another part are listed below under Mating features, with the fit each joint needs; open those by your printer's or process's clearance before making the part.

## Notes

- Closes a 2 in shell displacer like the standard cap and holds an Ø8 rod instead of an Ø3 one. The rod is the Ringbom drive: its cross-section (50.3 mm²) times the gas pressure minus air pressure is the force that moves the free displacer.
- The rod's D-flat end goes in the Ø8 socket, 12 deep, and the M4 grub seats on the flat.

## Mating features (exact size; open press / slide / run / socket by your process clearance, leave designed and clamp as drawn)

| feature | exact | mates with | fit | files |
|---|---|---|---|---|
| spigot | Ø44 × 3 | 2 in shell displacer bore | slide | all |
| rod socket | Ø8 × 12 | Ø8 rod D-flat end (M4 grub) | slide | all |
| grub hole | Ø3.3 | M4 tap drill | designed | all |

## Sizes

| part | spigot_mm | flange_mm | boss_mm | socket_mm |
|---|---|---|---|---|
| ringbom-cap-2in-r8 | Ø44 × 3 | Ø46 × 1.5 | Ø16 × 14 | Ø8 × 12 |

## Where the files are

- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Free STEP/STL (1 parts, CC BY 4.0, Xem Studio)

Index: https://xemstudio.com/files/hardware/tri-clamp-ringbom-displacer-cap/index.json

- ringbom-cap-2in-r8: [STEP](https://xemstudio.com/files/hardware/tri-clamp-ringbom-displacer-cap/ringbom-cap-2in-r8.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-ringbom-displacer-cap/ringbom-cap-2in-r8.stl) — Ringbom displacer cap: Ø44 × 3 spigot into a 2 in shell displacer, Ø46 × 1.5 flange, Ø16 boss to 18.5 with an Ø8 socket 12 deep and an M4 grub (Ø3.3)

## Questions

**How strong is the Ringbom push?**

50.3 mm² × the pressure difference: 0.5 N per 10 kPa, enough to lift about 51 g per 10 kPa.

## Fits with

- [Tri-clamp displacer: Ø33.6, Ø46 and Ø70.9 for 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-displacer/)
- [Tri-clamp gland caps, 2 in: end caps with a rod gland, an M5 port and a stop bridge or bell-crank post](https://xemstudio.com/objects/tri-clamp-rd-gland-caps/)
- [Build list: Tri-clamp rolling-diaphragm Ringbom, 2 in](https://xemstudio.com/objects/list-tri-clamp-rd-ringbom/)