Extension springs, wire Ø0.6 and Ø1.0 — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/extension-springs/  (CC BY 4.0)
Basis: Close-wound helical extension spring with a loop at each end; length over the loops
Catalog version: 2026-10-20

Sizes: see table below
- Close-wound bodies (coils at 1.02 × wire pitch so the turns stay separate) with a full loop each end; the length is over the two loops.
- 0.6 wire × OD 6 (ID 4.8), 30 over the loops, 20 coils; 1.0 wire × OD 10 (ID 8), 50 over the loops, 25 coils.
- Rate follows the same k = G d⁴ / (8 D³ n) as a compression spring, plus an initial tension from close winding; the loop ID is OD − 2 × wire and takes a hook pin.

file  wire Ø  OD  ID  length over loops  coils  index D/d
extension-d0.6-od6-l30  0.6  6  4.8  30  20  9.0
extension-d1-od10-l50  1.0  10  8.0  50  25  9.0

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Wikipedia: Spring (device) — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Spring_(device)
- McMaster-Carr: Compression springs (free STEP per part, for your own design use; no redistribution) — STEP, PDF — McMaster-Carr site terms [verify license at link] — https://www.mcmaster.com/products/compression-springs/
- Lee Spring: Spring design formulas — web — Lee Spring site [verify license at link] — https://www.leespring.com/learn-about-springs
- Long Earth Society: Engine and rig builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 2 parts): https://xemstudio.com/files/hardware/extension-springs/index.json
API: https://xemstudio.com/api/geometry?object=extension-springs