CD and HDD-platter flywheel hubs: Ø15 and Ø25 spigots for Ø3 / 5 / 8 shafts — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/flywheel-disc-hub/  (CC BY 4.0)
Basis: Spigot at the disc's centre hole (CD Ø15, 3.5 in HDD platter Ø25); bore at the shaft; M3 tap drill Ø2.5 for the set screw
Catalog version: 2026-10-20

Sizes: see table below
- A hub that carries a CD/DVD or a 3.5 in hard-drive platter as a flywheel. The spigot is the disc's centre hole exactly: Ø15 for a CD, Ø25 for a platter, 1.3 tall.
- As drawn, the spigot sits between a Ø(spigot + 8) × 2 collar below and the Ø(spigot + 8) hub body above (Ø23 for CD hubs, Ø33 for platter hubs), 12 mm overall.
- Bores: Ø3, Ø5 or Ø8 (fit: slide) for the shaft, with a Ø2.5 radial hole (M3 tap size) 6 mm above the lower collar for an M3 set screw.

file  disc  spigot  bore  outside  height
hub-cd-15-to-3  CD / DVD  15  3  23  12
hub-cd-15-to-5  CD / DVD  15  5  23  12
hub-cd-15-to-8  CD / DVD  15  8  23  12
hub-platter-25-to-5  3.5 in HDD platter  25  5  33  12
hub-platter-25-to-8  3.5 in HDD platter  25  8  33  12

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Wikipedia: Stirling engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Stirling_engine
- Long Earth Society: Can engine build — video, web — LES site — https://longearthsociety.com/engineering/
- Long Earth Society: Engine builds (videos and write-ups) — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 5 parts): https://xemstudio.com/files/hardware/flywheel-disc-hub/index.json
API: https://xemstudio.com/api/geometry?object=flywheel-disc-hub