# Standards for threads of machine screws- are there any coincidentally intercompatible examples? **URL:** \ **Category:** Factual Questions\ **Created:** [August 1, 2011, 7:23am UTC](https://boards.straightdope.com/t/standards-for-threads-of-machine-screws-are-there-any-coincidentally-intercompatible-examples/591015 "2011-08-01T07:23:41Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [August 1, 2011, 7:23am UTC](https://boards.straightdope.com/t/standards-for-threads-of-machine-screws-are-there-any-coincidentally-intercompatible-examples/591015/1 "2011-08-01T07:23:41Z")
Are there any examples of coincidental intercompatibility between the major screw thread types? (ISO, BSW, UTS, etc.) By intercompatibility, I mean, are there any cases where a nut of size X in thread standard Y fits properly (without crossing, binding or being intolerably loose) on a bolt of size P in thread standard Q? ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [August 1, 2011, 11:48am UTC](https://boards.straightdope.com/t/standards-for-threads-of-machine-screws-are-there-any-coincidentally-intercompatible-examples/591015/2 "2011-08-01T11:48:48Z")
5mm-.8 and #10-32 can be reasonably interchanged. ---
**Author:** ![Ronald\_C.Semone](https://avatars.discourse-cdn.com/v4/letter/r/cc9497/32.png) [@Ronald\_C.Semone](https://boards.straightdope.com/u/Ronald_C.Semone)\ **Post date:** [August 1, 2011, 11:56am UTC](https://boards.straightdope.com/t/standards-for-threads-of-machine-screws-are-there-any-coincidentally-intercompatible-examples/591015/3 "2011-08-01T11:56:23Z")
Am I the only one who read this title to mean “to hell with SDMB thread regulations”? ---
**Author:** ![KellyCriterion](https://avatars.discourse-cdn.com/v4/letter/k/b3f665/32.png) [@KellyCriterion](https://boards.straightdope.com/u/KellyCriterion)\ **Post date:** [August 1, 2011, 11:59am UTC](https://boards.straightdope.com/t/standards-for-threads-of-machine-screws-are-there-any-coincidentally-intercompatible-examples/591015/4 "2011-08-01T11:59:09Z")
> [@Ronald\_C.Semone](#): > > Am I the only one who read this title to mean “to hell with SDMB thread regulations”? No. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [August 1, 2011, 12:15pm UTC](https://boards.straightdope.com/t/standards-for-threads-of-machine-screws-are-there-any-coincidentally-intercompatible-examples/591015/5 "2011-08-01T12:15:47Z")
Perhaps a kindly mod could re-word the title to “Standards for threads of machine screws…”? ---
**Author:** ![EvilTOJ](https://avatars.discourse-cdn.com/v4/letter/e/ee59a6/32.png) [@EvilTOJ](https://boards.straightdope.com/u/EvilTOJ)\ **Post date:** [August 1, 2011, 2:25pm UTC](https://boards.straightdope.com/t/standards-for-threads-of-machine-screws-are-there-any-coincidentally-intercompatible-examples/591015/6 "2011-08-01T14:25:49Z")
No, leave it. I think IMHO and MPSIMS complement each other nicely. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [August 1, 2011, 3:31pm UTC](https://boards.straightdope.com/t/standards-for-threads-of-machine-screws-are-there-any-coincidentally-intercompatible-examples/591015/7 "2011-08-01T15:31:47Z")
From bitter experience I can state that the most likely result of attempts at such mixing are cross-threading, bindinbg, and letti ng loose at inconvenient times. Although a rare few might seem to be comptible, it’s realy best not to mix breeds. ---
**Author:** ![thelabdude](https://avatars.discourse-cdn.com/v4/letter/t/dc4da7/32.png) [@thelabdude](https://boards.straightdope.com/u/thelabdude)\ **Post date:** [August 1, 2011, 7:01pm UTC](https://boards.straightdope.com/t/standards-for-threads-of-machine-screws-are-there-any-coincidentally-intercompatible-examples/591015/8 "2011-08-01T19:01:31Z")
> [@Gary\_T](#): > > 5mm-.8 and #10-32 can be reasonably interchanged. I checked that out. The # 10 nut didn’t want to screw on the 5 mm very well. I think it could be forced. A 5 mm nut did easily screw on a #10 screw. I wouldn’t be surprised if it stripped easily too. I first noticed how well a 5/8’’ wrench fit a 16 mm nut. Of course as you halve it or double it, it still works well from 5/32’’ to 5/4’‘. I am sure the cap on the oil filter cartridge on my 02 Cavalier Ecotec was designed to fit a 32 mm socket. My old 5/4’’ socket fits fine. I have long used 15/16’’ wrenches on the 24 mm plugs on my truck. 19mm is very close to 3/4’'. Some lug wrenches are marked 19 mm, 3/4 ‘’. One that can trick you. The 10mm 1.0 brake line nuts only look very close to the 3/8’'-24 ones. I sometimes take advantage of the 5/16’‘-8mm thing. It is easy to find 5/16’’ rod. They take an 8mm-1.25 thread very well. Thus I don’t have to use inch crap on my all metric truck. ---
**Author:** ![Fourtyfold](https://avatars.discourse-cdn.com/v4/letter/f/f475e1/32.png) [@Fourtyfold](https://boards.straightdope.com/u/Fourtyfold)\ **Post date:** [August 1, 2011, 7:40pm UTC](https://boards.straightdope.com/t/standards-for-threads-of-machine-screws-are-there-any-coincidentally-intercompatible-examples/591015/9 "2011-08-01T19:40:53Z")
> [@thelabdude](#): > > …One that can trick you. The 10mm 1.0 brake line nuts only look very close to the 3/8’'-24 ones… I got caught out by this (or something very similar) a few months ago. Went to get some brake unions but the fools at a local car parts supplier must have had some mixed up in a box, as I found out once I started putting the pipes back on. Swine.