And i dont think GB is using UNC threads. They had BSW and its special pitch derivatives, BA and now are officially metric.
Edit: What i should have written: I dont think GB uses any UNIFIED NATIONAL threads...unless they manage to sneak their way in via some bloody OEM item
Maybe someone from GB can tell us how common UN threads are in GB?
I have a copy of British Standard 84 : 1956
Title: Parallel Screw Threads Of Whitworth Form.
On the back of the front page is written:
Ammendment No. 1, published 11 August, 1966
At a fully representative conference held on 23rd november, 1965 consideration was given to the action to be taken in relation to the move to metric as far as British Standards for screw threads were concerned and it was decided that:
British industry should be strongly recommended to to adopt the internationally agreed ISO metric threads or ISO inch threads but that ISO inch threads should be considered second choice. The implementation of this recommendation means that B.A:, BSF and BSW threads should become obsolete and should not be used in new designs.
ACCORDINGLY IT HAS BEEN AGREED THAT B.S. 84 BE RENDERED OBOLETE: IT WILL BE MADE OBSOLETE IN DUE COURSE.
I admit to not knowing if GB has arrived at "....... IN DUE COURSE".
Pipe threads with the Whitworth 55º flank form still are the widest used in the world to the best of knowledge. The old demonination for them was BSP and BSPT but have now been given an ISO denomination.
Oh, oh, more "spamming" coming up. BE WARNED
http://www.f-m-s.dk/3.05.pdf
For Whitworth type tapered threads there are 3 denominations:
R for external tapered thread
Rc for internal tapered threads
Rp for internal parallel threads (not to be confused with G type pipe threads which aren't intended to be leak proof on the thread itself).
G type pipe threads (in the link above) are usually sealed using an O-ring or gasket.
Gordon