T-mount (T2): M42 × 0.75 thread, 55 mm flange, thread rings — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/t-mount-t2/  (sheet CC BY 4.0)
Basis: Published numbers only (sources per row); thread drawn at the ISO 68-1 basic profile
Catalog version: 2026-10-20

Sizes: see table below
- Flange focal distance is the distance from the mount's reference face to the image plane; adapters and extension tubes must add exactly the difference between two mounts' flange distances to keep infinity focus.
- Telescopes, mirror lenses and microscope adapters end in a male M42 × 0.75 thread; a camera-specific T-ring carries the female thread and sets the 55 mm to the image plane.
- Not interchangeable with M42 × 1 (M42 screw mount).

parameter  value  from
flange focal distance  55 mm  T-mount (Wikipedia); Flange focal distance table
throat / inner diameter  not published in a source I could verify (left out)  —
thread  M42 × 0.75  standard
major Ø D  42.000 mm  standard
pitch P  0.75 mm  standard
pitch Ø D2 (basic)  41.513 mm  ISO 68-1 basic profile
minor Ø D1 (basic)  41.188 mm  ISO 68-1 basic profile
files  male and female ring sections, 8 turns, basic profile  —

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Wikipedia: T-mount: M42 x 0.75 thread, 55 mm flange focal distance — web — CC BY-SA 4.0 (text); dimensions are facts — https://en.wikipedia.org/wiki/T-mount
- Wikipedia: Flange focal distance (table of mounts) — web — CC BY-SA 4.0 (text); dimensions are facts — https://en.wikipedia.org/wiki/Flange_focal_distance
- Bureau of Indian Standards (via Public.Resource.Org): IS 4218 (Part 1):2001 ISO general purpose metric screw threads, basic profile (identical with ISO 68-1:1998): H = 0.866025404 P, 5H/8 = 0.541265877 P, 3H/8 = 0.324759526 P — web — Public.Resource.Org (public law); dimensions are facts — https://law.resource.org/pub/in/bis/S01/is.4218.1.2001.pdf
- ISO: ISO 68-1:1998 ISO general purpose screw threads — Basic profile — Part 1: Metric screw threads — web — Publisher's page; dimensions are facts — https://www.iso.org/standard/3707.html

Free files (CC BY 4.0, Xem Studio; STEP + STL, 2 parts): https://xemstudio.com/files/hardware/t-mount-t2/index.json
API: https://xemstudio.com/api/geometry?object=t-mount-t2