Quote Originally Posted by Alan de Enfield View Post
Do you have the actual specification for the bolt head sizes ?

I could never find the actual specification showing the required / start size(s) for each number simply the incremental increase by 'number'.

When I did the bolthead survey (many years ago) I posted this....

I wonder if anything new or more definitive on sizing has come to light since ?
Your survey of sizes emphasizes the point that without measuring the numbers become largely meaningless.