[spritely]

Originally Posted by GreatOldOne

Well, you'd need a thread pitch gauge and something to measure the bolt diameter. A vernier or digital calliper would do for the later:

http://www.maplin.co.uk/Module.aspx?ModuleNo=32198

and you can get thread gauges here:

http://www.axminster.co.uk/product.asp?pf_id=23483

You may find them cheaper on eBay - my digital calliper only cost me a 50p (but I did have to wait for it to come from Hong Kong).

Thanks for that, I have micrometer and a vernier and a thread gauge but it's a case of all the gear and no idea.
for instance, If the shank is 12mm then would that be a 12mm bolt or m12?
Then what is the method for finding out the size in UNF? as the bolt is I think in between metric sizes.