[Head type] 1. flat head 2. countersunk head 3. small countersunk head [Column type] 1. park rod type 2. groove 3. hexagonal (semi-hexagonal) [Stainless steel small countersunk head insert nuts Column type] Carbon steel, aluminum, stainless steel etc. [Product specifications] 1. M3, M4,M M5, M6, M8, M10, M12 2. 6-32, 8-32, 10-32, 1/4-20, 5/16-18, 3/8-16, 1/2-13