Thread = 12 TPI British Standard Whitworth
Countersunk Socket screws have an in-hex drive and are fastened using a hexagonal wrench also known as an Allen key.
The length is measured overall including the head, this is because the head sits in the material and therefore becomes part of the length.
Use Allen key size = 5/16"
Hardness = 36 HRC Min Tensile Strength = 170,000 PSI Min
