BS 1580 Unified Screw Threads

British Specification BS 1580 Unified Screw Threads
This is a bit confusion but BS1580 exists in two parts, but references to three parts can be found in historical documents. In 2007 BS1580-1:2007 was published which superceeded the previous BS 1580: Parts 1 & 2:1962. In the 1962 version Part 1 dealt with UNC, UNF and UNEF while part 2 dealt with UNS. In the 2007 version part 2 has been eliminated and part 1 deals with UN, UNC, UNF, UNEF and UNS.

BS 1580 Unified Screw Threads
BS 1580 Part 1 Screw threads with diameters 1/4 inch and larger – Requirements
BS 1580 Part 2 (obsolete) Combined with Part 1 in 2007.
BS 1580 Part 3 Screw threads with diameters below 1/4 inch – Requirements