HTD cold caps: 10 in tri-clamp caps with a 2 in ferrule at the centre — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/htd-cold-caps-10in/  (CC BY 4.0)
Basis: Fabrication spec: 10 in end cap profile at 15.875 (5/8 in) instead of the standard 12.19, a 2 in L14AM7-type ferrule welded on at the centre, bosses machined; exact geometry
Catalog version: 2026-10-20

Sizes: see table below
- Why thicker than a stock cap: at 6 bar gauge a stock 0.480 in cap sees 85 MPa and bows 0.35 mm; this 15.875 cap with its welded centre neck sees about 53 MPa and bows 0.16 mm, and it carries the welded ferrule, the guide boss and the NPT bosses.
- Main cap: the 2 in ferrule takes the bored power spool; inside it a Ø16 boss 20 tall carries the Ø6 displacer-rod guide (35.9 long through boss and plate); six Ø10 passages on r 16 let the gas between the chamber and the power cylinder; a 1/8 NPT boss at r 43 is the working-space gauge port.
- The flat top (inside Ø196.8, where the 20° back cone ends) carries the optional water tray.

part  thickness_mm  centre  ports
cold-cap-10in-main  15.875  2 in ferrule, Ø6 guide, 6 × Ø10  1/8 NPT gauge

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Steel & O'Brien: Sanitary products catalog 2024: 16AMP end caps 10 / 12 in (A 0.480, B 10.570 / 12.570 in); L14AM7 ferrules 1.500 in; clamp ratings 13MHHM, 13MHP, 13ASME — PDF — publisher's catalogue; dimensions cited, nothing copied — https://www.steelobrien.com/wp-content/uploads/2024/03/Sanitary-2024-FINAL.pdf
- McGraw-Hill: Young & Budynas, Roark's Formulas for Stress and Strain, 7th ed.: Table 8.1 (fixed–guided beam), Table 11.2 (circular plates under uniform pressure) — book — formulas are facts [verify license at link] — https://www.accessengineeringlibrary.com/content/book/9780071742474
- ASME: ASME B1.20.1 Pipe Threads (NPT): 1/8-27 and 1/4-18, tap drills Ø8.6 / Ø11.1 as on this site's thread envelopes — standard — ASME; dimensions are facts [verify license at link] — https://www.asme.org/codes-standards/find-codes-standards/b1-20-1-pipe-threads-general-purpose-inch
- 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-cold-caps-10in/index.json
API: https://xemstudio.com/api/geometry?object=htd-cold-caps-10in