The diameter specifies the shank and threaded outside side i.e. 1/4″ BSF bolt is 1/4″ dia. The length of any non-countersunk bolt/screw is always measured from beneath the head and countersunk bolts/screws are measured from the top of the head
Thread lengths vary over the size ranges but are generally 3/4″ to 1″. This is a rough guideline, if specific thread lengths are required then please contact us to check before ordering.
UNF bolts are often referred to by their spanner size rather than diameter i.e. 1/2″ AF (across flats) – 5/16″ dia, Please only order by specifying thread diameter.
Imperial Spanner Sizes and Threads