Alex,
I was trying to make it easy for Stephen, who, being from the U.S.of A.,is probably not very familiar with British thread forms.
While you are being so precise, it would be more accurate to say that BSC threads were used in some old leaky motorcycles.
How is that carrier coming together?
Stephen, as has been pointed out, It is referred to as Whitworth, or British Standard Whitworth.
1/2" is the problem size as it is 12 TPI where as 1/2" UNC has 13 TPI.
The other common sizes 1/4", 5/16", 3/8", and 7/16" are the same TPI as their counterparts (BSW and UNC)
This is not the case with the fine threads (BSF and UNF)