UNC or BSW - Verified

[obscura]

This is really to put this to bed - for me. Hope it helps others with similar doubts.

SW it seems provide 1/4" BSW bolts for their dovetails and at first try, the bolt went tight halfway through. Paint in thread? No. OK, you can continue to run it through with care if you want - but I am a purist. Also, some web sites declare 1/4" BSW is the standard camera thread.

Checking archived threads here in SGL brought up 1/4" UNC. I got me some of these from Namrick and proved that the true camera thread is UNC as is the SW thread.

Both are 1/4" 20tpi but UNC are 60 as against the BSW 55 degrees. I now understand that the UNC was developed in the USA for car manufacture which was followed up in the UK with the ANC (I think that what it was).

Thanks to the earlier thread for the lead here.

Ye Olde Git

[Peter Drew]

This similarity of fit holds good for most BSW/UNC sizes apart from 1/2" which is one thread per inch pitch different.