Ø400 flywheel on a Ø12 shaft — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/htd-flywheel-400/  (CC BY 4.0)
Basis: Exact geometry
Catalog version: 2026-10-20

Sizes: see table below
- Rim r 175..200 × 30 wide, 5 web, Ø50 × 40 hub, two M6 grubs. J = 0.104 kg·m² (3.9 kg) at 2.7 g/cm³, 0.305 kg·m² (11.3 kg) at 7.9 g/cm³.
- On the HTD it hangs outside the seal cap at x 186.5..226.5; a slow flat engine needs the inertia (the speed swing is on the list page).

od_mm  rim_mm  web_mm  hub_mm  J_kgm2_2.7  J_kgm2_7.9
400.0  175–200 × 30  5.0  Ø50 × 40  0.104  0.305

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, 1 parts): https://xemstudio.com/files/hardware/htd-flywheel-400/index.json
API: https://xemstudio.com/api/geometry?object=htd-flywheel-400