# 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

> What clearance does a ring-less Stirling power piston need in a 2 inch tri-clamp spool, and how do I get it?

- Category: Stirling engines › Tri-clamp engine parts
- Kind: Hardware
- Basis: 16 ga ASME BPE tube bores (1.5 in = 34.8 mm, 2 in = 47.5, 3 in = 72.9); finished ring-less piston fit 0.02–0.05 mm diametral (graphite-in-glass and lapped-aluminium Stirling practice); FDM print-and-lap offsets from the Xem Studio calibration coupons
- Page: https://xemstudio.com/objects/tri-clamp-power-pistons/ · JSON: https://xemstudio.com/api/geometry?object=tri-clamp-power-pistons · Plain text: https://xemstudio.com/objects/tri-clamp-power-pistons/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses

## Notes

- A Stirling power piston has no ring and no O-ring: the seal is the fit. Finished diametral clearance 0.02–0.05 mm; the test is that the piston falls slowly through the spool under its own weight with the far end open and holds for several seconds with it closed.
- You cannot print that fit. Print the closest offset your printer makes (f010/f020/f030 = 0.10/0.20/0.30 mm under bore after the hole/pin coupons have set your slicer), or the 'lap' version 0.10 mm over, then lap it in: 800 → 1500 grit wet, then metal polish, turning the piston in the actual spool on the lapping handle. PETG laps well; PLA galls. Finish with a dry graphite rub (pencil) and run it dry; oil adds friction and stiction in a Stirling.
- Length 1.2 × bore keeps it from cocking: the two 8 mm lands at the ends carry the fit; the 0.4 mm relief between them halves the rubbing area and traps dust. Wrist pin Ø3 (dowel-pins-metric) at 0.42 L, con-rod small end with a 623 bearing from the crank kit; the skirt is open so the rod swings inside it.
- Where it goes: beta engine (piston and displacer in one spool, displacer rod through the piston's wrist-pin gap), alpha (two spools at 90°, a piston in each, no displacer), or a big low-compression gamma (same-bore power cylinder: 1:1 swept ratio, suits an LTD on a hot plate). For a high-ratio gamma use the Ø20 piston from the power-cylinder entry instead.
- The -rod variants (f020 and lap) have a Ø5 crown boss for a dry 3 × 5 × 6 bushing (graphite-bronze, PTFE, or sintered bronze degreased in acetone; no oil) so a Ø3 displacer rod runs through the piston on a clearance fit: that is the beta / rhombic / free-piston piston. The piston plug in the tri-clamp linkage kit drops into the skirt, is retained by the two wrist-pin dowels, and carries the 5 mm tube piston rod with the displacer rod inside it.
- Mass: the 2 in piston prints at ~21 g in PETG (16.8 cm³); keep it light, it is the moving mass the flywheel has to swing.
- Linkage, designed so nothing else is needed: the crank frame is an ISO 2852 cap with a con-rod window and two bearing towers, so a stock clamp holds it on the spool's open ferrule; a Ø8 shaft (shafts entry, 80–100 mm) runs in two 608s; two crank webs (Ø8 bore, M3 grub) carry a Ø3 pin at stroke/2 between them; the con-rod runs on 623s at both ends. Order along the shaft: tower · web · rod · web · tower, 1 mm gaps. The flywheel (Ø80–100, Ø8 bore, crank kit) and an 8 mm collar go outside one tower.
- Geometry: piston skirt flush with the ferrule face at bottom dead centre, so the lands never leave the bore; rod centres = wrist-pin height + crank height + stroke/2 (1.5 in: 58, 2 in: 70, 3 in: 95); rod angle under 11°. Stroke 16 / 24 / 36 mm = 0.46 × bore, which gives a 2 in alpha or beta ~42 mL swept per cylinder.
- Wrist pin: Ø3 rod cut to the length in the table (drill rod, music wire or a 3 mm dowel for 1.5 in); it is retained by the spool bore, no clips. Set the webs 180° apart on an alpha's second cylinder, or add the counterweighted cranks entry's webs for balance.
- LES: the piston the tri-clamp beta and alpha engines run in a stock spool with no liner.

## Sizes

| spool | bore_mm | piston_od_mm | length_mm | offset_mm | wrist_pin_z_mm |
|---|---|---|---|---|---|
| 1.5 | 34.800000000000004 | 34.9 | 42 | +0.10 | 17.6 |
| 1.5 | 34.800000000000004 | 34.7 | 42 | -0.10 | 17.6 |
| 1.5 | 34.800000000000004 | 34.6 | 42 | -0.20 | 17.6 |
| 1.5 | 34.800000000000004 | 34.5 | 42 | -0.30 | 17.6 |
| 2 | 47.5 | 47.6 | 56 | +0.10 | 23.5 |
| 2 | 47.5 | 47.4 | 56 | -0.10 | 23.5 |
| 2 | 47.5 | 47.3 | 56 | -0.20 | 23.5 |
| 2 | 47.5 | 47.2 | 56 | -0.30 | 23.5 |
| 3 | 72.9 | 73.0 | 88 | +0.10 | 37.0 |
| 3 | 72.9 | 72.8 | 88 | -0.10 | 37.0 |
| 3 | 72.9 | 72.7 | 88 | -0.20 | 37.0 |
| 3 | 72.9 | 72.6 | 88 | -0.30 | 37.0 |

## Linkage

| spool | stroke_mm | crank_height_mm | rod_centres_mm | wrist_pin_z_mm | tower_gap_mm | bought |
|---|---|---|---|---|---|---|
| 1.5 | 16.0 | 32.0 | 58 | 17.6 | 21.0 | Ø8 × 80 shaft, 2 × 608, 2 × 623, Ø3 pin × 19, Ø3 wrist pin × 29 |
| 2 | 24.0 | 34.0 | 70 | 23.5 | 21.0 | Ø8 × 80 shaft, 2 × 608, 2 × 623, Ø3 pin × 19, Ø3 wrist pin × 42 |
| 3 | 36.0 | 40.0 | 95 | 37.0 | 21.0 | Ø8 × 80 shaft, 2 × 608, 2 × 623, Ø3 pin × 19, Ø3 wrist pin × 68 |

## Where the files are

- Long Earth Society: [Tri-clamp Stirling engine builds](https://longearthsociety.com/engineering/) — web, video — LES site
- James R. Senft: [An Introduction to Stirling Engines (piston fit and leakage)](https://www.stirlingengine.com/) — book — Moriya Press (verify at link)
- ASME: [BPE tube dimensions (16 ga sanitary tube)](https://www.asme.org/codes-standards/find-codes-standards/bpe-bioprocessing-equipment) — standard — ASME (verify at link)

## Free STEP/STL (30 parts, CC BY 4.0, Xem Studio)

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

- piston-1.5in-lap: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-1.5in-lap.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-1.5in-lap.stl) — 1.5 in full-bore piston Ø34.90 × 42 (lapping stock, +0.10 over bore), two 8 mm lands, Ø3 wrist pin at 17.6 mm, open skirt; print crown up, 0.1 mm layers
- piston-1.5in-lap-rod: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-1.5in-lap-rod.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-1.5in-lap-rod.stl) — 1.5 in piston as above with a Ø5.0 centre bore and boss in the crown for a dry 3 × 5 × 6 bushing (no oil): the displacer rod passes through it (beta, rhombic, free-piston)
- piston-1.5in-f010: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-1.5in-f010.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-1.5in-f010.stl) — 1.5 in full-bore piston Ø34.70 × 42 (0.10 mm under bore), two 8 mm lands, Ø3 wrist pin at 17.6 mm, open skirt; print crown up, 0.1 mm layers
- piston-1.5in-f020: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-1.5in-f020.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-1.5in-f020.stl) — 1.5 in full-bore piston Ø34.60 × 42 (0.20 mm under bore), two 8 mm lands, Ø3 wrist pin at 17.6 mm, open skirt; print crown up, 0.1 mm layers
- piston-1.5in-f020-rod: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-1.5in-f020-rod.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-1.5in-f020-rod.stl) — 1.5 in piston as above with a Ø5.0 centre bore and boss in the crown for a dry 3 × 5 × 6 bushing (no oil): the displacer rod passes through it (beta, rhombic, free-piston)
- piston-1.5in-f030: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-1.5in-f030.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-1.5in-f030.stl) — 1.5 in full-bore piston Ø34.50 × 42 (0.30 mm under bore), two 8 mm lands, Ø3 wrist pin at 17.6 mm, open skirt; print crown up, 0.1 mm layers
- lapping-handle-1.5in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/lapping-handle-1.5in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/lapping-handle-1.5in.stl) — 1.5 in lapping handle: plug into the open skirt and a T-bar to turn the piston in the spool with lapping compound
- crank-frame-1.5in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/crank-frame-1.5in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/crank-frame-1.5in.stl) — 1.5 in crank frame: ISO 2852 cap face (clamps to the spool with a stock clamp), Ø21 con-rod window, two towers with 608 pockets for a Ø8 crankshaft 32 mm above the face, 21 mm between towers
- crank-web-1.5in-s16: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/crank-web-1.5in-s16.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/crank-web-1.5in-s16.stl) — 1.5 in crank web: Ø8 bore with M3 grub, Ø3 pin at 8 mm (16 mm stroke); print two
- conrod-1.5in-58: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/conrod-1.5in-58.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/conrod-1.5in-58.stl) — 1.5 in con-rod, 58 mm centres, 5 mm thick, 623 pockets both ends (wrist pin and crank pin Ø3)
- piston-2in-lap: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-2in-lap.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-2in-lap.stl) — 2 in full-bore piston Ø47.60 × 56 (lapping stock, +0.10 over bore), two 8 mm lands, Ø3 wrist pin at 23.5 mm, open skirt; print crown up, 0.1 mm layers
- piston-2in-lap-rod: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-2in-lap-rod.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-2in-lap-rod.stl) — 2 in piston as above with a Ø5.0 centre bore and boss in the crown for a dry 3 × 5 × 6 bushing (no oil): the displacer rod passes through it (beta, rhombic, free-piston)
- piston-2in-f010: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-2in-f010.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-2in-f010.stl) — 2 in full-bore piston Ø47.40 × 56 (0.10 mm under bore), two 8 mm lands, Ø3 wrist pin at 23.5 mm, open skirt; print crown up, 0.1 mm layers
- piston-2in-f020: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-2in-f020.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-2in-f020.stl) — 2 in full-bore piston Ø47.30 × 56 (0.20 mm under bore), two 8 mm lands, Ø3 wrist pin at 23.5 mm, open skirt; print crown up, 0.1 mm layers
- piston-2in-f020-rod: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-2in-f020-rod.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-2in-f020-rod.stl) — 2 in piston as above with a Ø5.0 centre bore and boss in the crown for a dry 3 × 5 × 6 bushing (no oil): the displacer rod passes through it (beta, rhombic, free-piston)
- piston-2in-f030: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-2in-f030.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-2in-f030.stl) — 2 in full-bore piston Ø47.20 × 56 (0.30 mm under bore), two 8 mm lands, Ø3 wrist pin at 23.5 mm, open skirt; print crown up, 0.1 mm layers
- lapping-handle-2in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/lapping-handle-2in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/lapping-handle-2in.stl) — 2 in lapping handle: plug into the open skirt and a T-bar to turn the piston in the spool with lapping compound
- crank-frame-2in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/crank-frame-2in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/crank-frame-2in.stl) — 2 in crank frame: ISO 2852 cap face (clamps to the spool with a stock clamp), Ø28 con-rod window, two towers with 608 pockets for a Ø8 crankshaft 34 mm above the face, 21 mm between towers
- crank-web-2in-s24: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/crank-web-2in-s24.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/crank-web-2in-s24.stl) — 2 in crank web: Ø8 bore with M3 grub, Ø3 pin at 12 mm (24 mm stroke); print two
- conrod-2in-70: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/conrod-2in-70.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/conrod-2in-70.stl) — 2 in con-rod, 70 mm centres, 5 mm thick, 623 pockets both ends (wrist pin and crank pin Ø3)
- piston-3in-lap: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-3in-lap.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-3in-lap.stl) — 3 in full-bore piston Ø73.00 × 88 (lapping stock, +0.10 over bore), two 8 mm lands, Ø3 wrist pin at 37.0 mm, open skirt; print crown up, 0.1 mm layers
- piston-3in-lap-rod: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-3in-lap-rod.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-3in-lap-rod.stl) — 3 in piston as above with a Ø5.0 centre bore and boss in the crown for a dry 3 × 5 × 6 bushing (no oil): the displacer rod passes through it (beta, rhombic, free-piston)
- piston-3in-f010: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-3in-f010.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-3in-f010.stl) — 3 in full-bore piston Ø72.80 × 88 (0.10 mm under bore), two 8 mm lands, Ø3 wrist pin at 37.0 mm, open skirt; print crown up, 0.1 mm layers
- piston-3in-f020: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-3in-f020.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-3in-f020.stl) — 3 in full-bore piston Ø72.70 × 88 (0.20 mm under bore), two 8 mm lands, Ø3 wrist pin at 37.0 mm, open skirt; print crown up, 0.1 mm layers
- piston-3in-f020-rod: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-3in-f020-rod.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-3in-f020-rod.stl) — 3 in piston as above with a Ø5.0 centre bore and boss in the crown for a dry 3 × 5 × 6 bushing (no oil): the displacer rod passes through it (beta, rhombic, free-piston)
- piston-3in-f030: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-3in-f030.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-3in-f030.stl) — 3 in full-bore piston Ø72.60 × 88 (0.30 mm under bore), two 8 mm lands, Ø3 wrist pin at 37.0 mm, open skirt; print crown up, 0.1 mm layers
- lapping-handle-3in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/lapping-handle-3in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/lapping-handle-3in.stl) — 3 in lapping handle: plug into the open skirt and a T-bar to turn the piston in the spool with lapping compound
- crank-frame-3in: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/crank-frame-3in.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/crank-frame-3in.stl) — 3 in crank frame: ISO 2852 cap face (clamps to the spool with a stock clamp), Ø44 con-rod window, two towers with 608 pockets for a Ø8 crankshaft 40 mm above the face, 21 mm between towers
- crank-web-3in-s36: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/crank-web-3in-s36.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/crank-web-3in-s36.stl) — 3 in crank web: Ø8 bore with M3 grub, Ø3 pin at 18 mm (36 mm stroke); print two
- conrod-3in-95: [STEP](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/conrod-3in-95.step) · [STL](https://xemstudio.com/files/hardware/tri-clamp-power-pistons/conrod-3in-95.stl) — 3 in con-rod, 95 mm centres, 5 mm thick, 623 pockets both ends (wrist pin and crank pin Ø3)

## How it fits

### Goes in or on
- [Tri-clamp spool (two ferrules on a tube), 1.5 and 2 inch](https://xemstudio.com/objects/tri-clamp-spool/): runs in the 16 ga bore (34.8 / 47.5 / 72.9) with no ring
- [Tri-clamp cups: closed-end spools (ferrule on a capped tube), 1.5, 2 and 3 in](https://xemstudio.com/objects/tri-clamp-cups/): same bore, closed end: the alpha or test cylinder

### Connects to
- [Stirling linkage fittings: rod clevises, shaft adapter, 625 crank stands, Ø3 crank discs, rhombic frame heads](https://xemstudio.com/objects/stirling-linkage-fittings/): rod clevis on the 5 mm tube rod; rhombic frame head for a beta
- [Rhombic drive kit (Philips beta Stirling): twin crank gears, links, yokes, frame](https://xemstudio.com/objects/rhombic-drive-kit/): the -rod piston's tube rod into the lower yoke
- [Tri-clamp free-piston kit: flexure head, stack ring, hub collars and piston plug for 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-free-piston-kit/): piston plug + tube rod onto the flexure stack
- [Crank discs, connecting rods and flywheels for model engines](https://xemstudio.com/objects/crank-conrod-flywheel-kit/): flywheel for the crank frame's Ø8 shaft

### Alternatives
- [Power cylinder liners, piston blanks, crosshead and guide (the non-syringe power piston)](https://xemstudio.com/objects/power-cylinder-piston-crosshead/): small Ø16–30 piston blanks and liners for a high-ratio gamma
- [Free-piston Stirling core: displacer, power piston, liner, gas spring, stops, clearance-seal and tuning tables](https://xemstudio.com/objects/free-piston-core/): Ø30 / Ø40 piston blanks in their own liner
- [Syringe pistons: ring-less printed pistons with a con-rod fork for 10, 20 and 30 mL syringe barrels](https://xemstudio.com/objects/syringe-pistons/): 10–30 mL syringe barrels as the power cylinder

### Also needed
- [Stirling shafts and rods: Ø3 rods, Ø5 / Ø8 D-flat crankshafts, Ø5 tube rods, Ø3 pins, thrust spacers](https://xemstudio.com/objects/stirling-shafts-and-rods/): Ø8 D-flat crankshaft for the crank frame, Ø3 pins, spacers
- [Nut-weighted flywheels: Ø100–200 with hex pockets for M8, M10, M12, 3/8 and 1/2 in nuts](https://xemstudio.com/objects/nut-weighted-flywheels/): Ø8-hub flywheel on the crank frame
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/): Ø3 × 16 wrist pins
- [Ball bearings, 683 to 6210 and flanged F6xx (ISO 15)](https://xemstudio.com/objects/ball-bearings-metric/): 608 for the crank frame, 623 in the con-rod
- [Shafts, D-flats, set-screw collars, E-clips (DIN 6799) and circlips (DIN 471)](https://xemstudio.com/objects/shaft-collars-clips-and-shafts/): Ø8 crankshaft, collars
- [Bearing housings and linear supports: KP08, KFL08, SK8, SC8UU, V-wheels, sleeve bushings](https://xemstudio.com/objects/bearing-housings-and-rod-supports/): 3 × 5 × 6 bushing in the -rod piston's crown
- [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 the crank frame to the spool
- [Printer calibration coupons: hole, pin, nut-trap, T-slot tongue and bearing-pocket gauges](https://xemstudio.com/objects/printer-calibration-coupons/): set the slicer before printing a fit

## Questions

**How much clearance does a Stirling piston need without rings?**

0.02–0.05 mm on diameter when finished. It should sink slowly through the open spool under its own weight and hold for seconds with the end closed.

**Which piston file do I print for a 2 inch spool?**

Start with piston-2in-f020 (Ø47.30 for the 47.5 bore). If it drops straight through, print f010; if it will not enter, f030. Then lap to the final fit in the spool itself.

**How do I lap a printed piston?**

Plug the lapping handle into the open skirt, wet 800 grit wrapped on the piston, turn and stroke it in the real spool, step to 1500 and polish, wash, rub pencil graphite in and run it dry.

**Why not an O-ring?**

An O-ring's friction eats most of a model Stirling's few hundred milliwatts; the piston would stall. The fit is the seal, as in graphite-and-glass engines.

**How do I connect the piston to a crankshaft?**

Print the crank frame for your spool size, two crank webs and the con-rod; clamp the frame to the spool's open ferrule with a stock clamp, press two 608s into the towers, run a Ø8 shaft through, set the webs with the Ø3 pin between them and the con-rod on it, and the other end of the rod on the Ø3 wrist pin in the piston. Flywheel outside one tower.

**Why two lands with a relief between?**

Only the ends touch the bore, so friction halves while the full length still keeps the piston aligned; dust collects in the relief instead of scoring the bore.

## Fits with

- [Tri-clamp spool (two ferrules on a tube), 1.5 and 2 inch](https://xemstudio.com/objects/tri-clamp-spool/)
- [Tri-clamp cups: closed-end spools (ferrule on a capped tube), 1.5, 2 and 3 in](https://xemstudio.com/objects/tri-clamp-cups/)
- [Tri-clamp displacers and engine heads: 1.5, 2 and 3 in spools](https://xemstudio.com/objects/tri-clamp-displacers-and-heads/)
- [Dowel pins, 2–6 mm (ISO 2338 / DIN 6325)](https://xemstudio.com/objects/dowel-pins-metric/)
- [Shafts, D-flats, set-screw collars, E-clips (DIN 6799) and circlips (DIN 471)](https://xemstudio.com/objects/shaft-collars-clips-and-shafts/)
- [Ball bearings, 683 to 6210 and flanged F6xx (ISO 15)](https://xemstudio.com/objects/ball-bearings-metric/)
- [Crank discs, connecting rods and flywheels for model engines](https://xemstudio.com/objects/crank-conrod-flywheel-kit/)
- [Counterweighted crank discs, crank webs and bolt-on counterweights](https://xemstudio.com/objects/counterweighted-cranks/)
- [Power cylinder liners, piston blanks, crosshead and guide (the non-syringe power piston)](https://xemstudio.com/objects/power-cylinder-piston-crosshead/)
- [Printer calibration coupons: hole, pin, nut-trap, T-slot tongue and bearing-pocket gauges](https://xemstudio.com/objects/printer-calibration-coupons/)
- [Alpha V-twin: 90° two-pin crank discs, V block, transfer tee](https://xemstudio.com/objects/alpha-twin-crank-90/)