Test-tube marble engine rocker: tube and glass-syringe rings on a pivot — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/marble-engine-rocker/  (CC BY 4.0)
Basis: My geometry: Ø25 ring at the 25 × 150 tube's OD (DURAN / KIMBLE 25 × 150), Ø15.40 ring at the 5 mL glass barrel's published OD (KD Scientific); tube and syringe on one axis so the transfer line never bends
Catalog version: 2026-10-20

Sizes: see table below
- The tube (hot end out, stopper toward the pivot) and the 5 mL glass syringe (tip toward the stopper) sit on one axis 18 above the pivot; the 4 mm tube through the stopper and a 50 mm silicone tube join them in a straight line, so nothing flexes as it rocks.
- Pivot: Ø3 bore for a dowel-3x30 through two beam-pivot-post-60 posts (hub 10 wide between them). Lever pin Ø3 at (35, −45) from the pivot for the 170 mm rocking link; with a 7.5 mm crank throw the rocker swings -7.9° to +7.9°.
- Rings: Ø25 × 12 for the tube, Ø15.40 × 12 for the syringe barrel, each with an M3 grub (set-m3x4, Ø2.5 tapped) that reaches the glass.

feature  value
tube ring  Ø25 × 12
syringe ring  Ø15.40 × 12
axis above pivot  18
lever pin  (35, −45), Ø3
swing  -7.9..7.9°

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- DWK / DURAN (via Parkes Scientific): DURAN test tubes 26 130: 25 × 150 mm, 55 mL, wall 1.0–1.2 mm (cat. 261303308) — web — listing [verify license at link] — https://parkesscientific.com/p/duran-26130-test-tubes-with-beaded-rim
- DWK Life Sciences: KIMBLE reusable culture tube 25 × 150 mm, 55 mL (45048-25150) — web — manufacturer page [verify license at link] — https://www.dwk.com/na/kimble-reusable-culture-tube-25-x-150-mm-55-ml-45048-25150
- KD Scientific: Full Line of Glass Syringes, rev. A (order codes 78-0871 to 78-0880): piston OD, barrel OD D1, barrel collar D2, piston collar D3, length L — PDF — manufacturer datasheet [verify license at link] — https://www.kdscientific.com/media/brochures/KDS%20Glass%20Syringe%20Datasheet.pdf
- Wikipedia: Stirling engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Stirling_engine
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/marble-engine-rocker/index.json
API: https://xemstudio.com/api/geometry?object=marble-engine-rocker