These are stainless steel hex countersunk bolts. ·Use a hex wrench suitable for tightening (please use a wrench with the size of the hex hole diagonal (s)); The nominal length of the hex hole countersunk bolt is referred to as the total length (L), including the countersunk head. In addition to "countersunk bolts" with hex holes, they are also described as "countersunk caps" and "countersunk cap screws".