12-13-2016, 05:53 AM
I believe that Andrew is correct but your comment about it looking like a M8 bolt and stating it is Whitworth made me wonder. If I am correct, UN and Whitworth (British Standard Whitworth [BSW]) major diameter and tpi were the same until they got to 1/2" and above. 1/2" UNC is 13tpi where 1/2" Whitworth is 12tpi.
British Standard Fine (BSF) is (as the name suggests) the finer version of Whitworth threads and I believe that 5/8" Whitworth is actually 14tpi, as opposed to the 5/8" UNF 18tpi. There was also a British Standard Cycle (BSC) but that is best left alone!
I'm guessing this is the type of thread gauge that you are using:
![[Image: 11288.jpg]](http://www.myford.co.uk/acatalog/11288.jpg)
If so, I would still confirm the major diameter of the bolt with a micrometer or caliper. Even a drill index will work. The reason that I wouldn't simply assume that it is a standard (if there is such a thing) fastener, is that there are so many variations. I think I have 5/16" bolts in at least 5 different thread pitches.
Pictures of what you are using and what you are measuring would help.
British Standard Fine (BSF) is (as the name suggests) the finer version of Whitworth threads and I believe that 5/8" Whitworth is actually 14tpi, as opposed to the 5/8" UNF 18tpi. There was also a British Standard Cycle (BSC) but that is best left alone!
I'm guessing this is the type of thread gauge that you are using:
If so, I would still confirm the major diameter of the bolt with a micrometer or caliper. Even a drill index will work. The reason that I wouldn't simply assume that it is a standard (if there is such a thing) fastener, is that there are so many variations. I think I have 5/16" bolts in at least 5 different thread pitches.
Pictures of what you are using and what you are measuring would help.
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