Machinerys handbook lists it as 5/8 -16 UN between UNC and UNF. From my
experience with the A series it uses unified threads and not BSW / BSF.
Are you doing something special with the engine or do you just require a
replacement.

Brian wrote:

The crank pulley bolt on a BMC A-series engine is 5/8" 16 TPI. I can't seem
to match that to any thread series. Is it a custom truly non-standard
thread, or is there a hope of finding a source for a 1.5" long bolt in that
thread?

Thanks, Brian