Once a while I receive questions about adding extra screw to the order or if screw they can be purchased separately. Everything is fine until we start to discus head type and screw length. Industry do not fallow one standard and this confuse few people.
There is 3 common type screws .
Socket head cap screw. Screw dimension (length) is measured under head. In sample above this is 1/4-20 SHCS 5/8 length