Syringe pistons: ring-less printed pistons with a con-rod fork for 10, 20 and 30 mL syringe barrels — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/syringe-pistons/  (CC BY 4.0)
Basis: Barrel IDs from the plastic-syringes entry (10 mL 14.5, 20 mL 19.1, 30 mL 21.7 mm); same two-land, print-and-lap method as the tri-clamp power pistons
Catalog version: 2026-10-20

Sizes: see table below
- The rubber tip of a syringe plunger seals by squeezing the wall: far too much friction for a Stirling. Throw the plunger away and run a printed piston in the barrel instead, lapped to fit like the tri-clamp pistons (sinks slowly under its own weight, holds with the tip capped).
- Each piston has a 5 mm fork slot (exact: the con-rod thickness; see Mating features) open to the bottom and a Ø3 pin hole across it at 0.45 L: the Ross yoke kit's conrod-45 / conrod-60 (5 mm thick, Ø3 ends) or the crank kit's con-rods drop straight in on a 3 × 12 dowel. The fork keeps the con-rod inside the barrel's footprint, so the piston can enter the barrel past the pin.
- Fits: f008 / f015 are 0.08 / 0.15 mm under the barrel; lap is 0.08 over, to lap down. Plastic barrels vary by brand, so measure yours with calipers and pick the closest.
- Used by: the Ross yoke alpha (cylinder block for two 10 mL barrels), the alpha 90° V-block, the gamma power head (10 mL socket) and the can engine.
- LES: the syringe engines' pistons.

syringe  barrel_id_mm  piston_od_mm  length_mm  offset_mm  pin_z_mm
10ml  14.5  14.58  19  +0.08  8.6
10ml  14.5  14.42  19  -0.08  8.6
10ml  14.5  14.35  19  -0.15  8.6
20ml  19.1  19.18  25  +0.08  11.2
20ml  19.1  19.02  25  -0.08  11.2
20ml  19.1  18.95  25  -0.15  11.2
30ml  21.7  21.78  28  +0.08  12.6
30ml  21.7  21.62  28  -0.08  12.6
30ml  21.7  21.55  28  -0.15  12.6

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 9 parts): https://xemstudio.com/files/hardware/syringe-pistons/index.json
API: https://xemstudio.com/api/geometry?object=syringe-pistons