Library › Cameras & lenses › Lens mounts & filter threads ·

C-mount (1-32 UN): 17.526 mm flange, thread rings; CS-mount

Name: C-mount (1-32 UN): 17.526 mm flange, thread rings; CS-mount dimension sheet
Creator: Xem Studio
License: https://creativecommons.org/licenses/by/4.0/

What is the C-mount flange focal distance? · Standard part · basis: Published numbers only (sources per row); thread drawn at the ISO 68-1 basic profile

Also called: c mount thread, 1-32 un thread, c mount flange distance, cs mount, c to cs spacer, c mount adapter stl

Exact dimensions. True size, with no printing tolerance added.

sizes: 8 in table

Notes

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.
Machine-vision, CCTV, cine and microscope cameras: 1 in diameter, 32 threads per inch, designated 1-32 UN 2A (ISO 10935, interfacing connection type C). The lens has the male thread.
CS-mount uses the same thread with a 12.526 mm flange distance: a C lens fits a CS camera with a 5 mm spacer, a CS lens does not focus on a C camera.
The Unified thread basic profile is the same 60° profile as ISO 68-1, so the same formulas apply with P = 25.4/32 = 0.79375 mm.

C-mount (1-32 UN): 17.526 mm flange, thread rings; CS-mount size chart

parameter	value	from
flange focal distance	17.526 mm (0.6900 in); CS-mount 12.526 mm	ISO 10935 via Wikipedia
throat / inner diameter	not published in a source I could verify (left out)	—
thread	1-32 UN (2A)	standard
major Ø D	25.400 mm	standard
pitch P	0.79375 mm	standard
pitch Ø D2 (basic)	24.884 mm	ISO 68-1 basic profile
minor Ø D1 (basic)	24.541 mm	ISO 68-1 basic profile
files	male and female ring sections, 8 turns, basic profile	—

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

Wikipedia (citing ISO 10935:2009)	C mount: 1-32 UN 2A thread, 17.526 mm flange focal distance; CS mount 12.526 mm	web	CC BY-SA 4.0 (text); dimensions are facts
Wikipedia	Unified Thread Standard (ASME B1.1): same 60° basic profile as ISO 68-1	web	CC BY-SA 4.0 (text); dimensions are facts
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

Free files

★ Free files 2 parts. Generated by Xem Studio from the standard; threads are plain cylinders at major diameter. CC BY 4.0. index.json

1-32un-male-ring	1-32 UN (C-mount) external thread ring section: ISO 68-1 basic profile, major Ø25.4, pitch Ø24.884, minor Ø24.541, pitch 0.79375; 6.35 long (8 turns), bore Ø20.541 (wall is a design choice); exact nominal, no tolerance	STEP · STL
1-32un-female-ring	1-32 UN (C-mount) internal thread ring section: ISO 68-1 basic profile, minor Ø24.541, pitch Ø24.884, major Ø25.4, pitch 0.79375; 6.35 long (8 turns), outside Ø29.4 (design choice); exact nominal, no tolerance	STEP · STL

Let your AI pull this. Add https://xemstudio.com/mcp to Claude, ChatGPT, Cursor or any MCP client (free, no account, one minute) and it can look up exact sizes, mating fits and free STEP/STL from every chat.

Set it up →

Plain text: sheet.txt · JSON: /api/geometry?object=c-mount