Socket cap screws.
UNC thread pattern.
A2 stainless steel.
10UNC - 24tpi; allen key size 5/32"
1/4UNC - 20tpi; allen key size 3/16".
5/16UNC - 18tpi; allen key size 1/4".
3/8UNC - 16tpi; allen key size 5/16".
7/16UNC - 14tpi; allen key size 3/8"
1/2UNC - 13tpi; allen key size 3/8"