No. 5 or No. 4 bolt?

[Peter Laidler]

Given that info Ensci and others, it ties in together with the fact that as the hole was permitted in order to make best use of the manufacturers facilities, such as a holding or locating facility, then the size of the hole was also fairly academic too - within reason of course. Hence the variation in hole size

I seem to remember that the change in finish during 1968 that affected the interchangeable No4 and 5 bolt, as mentioned by Ensci was the deembrttlement of the phosphate finish of the bolt