Strech series 1,Super hardness 2,Materials: HSS M2, SKH9, SKD11 3, ... material of header punches you need or the material of screw you need.2. the head shape/type & recess of header ... standard you used, for examples:JIS,ANSI or DIN4. the screw size & header punch dimension,for example: M3.0,D12*25 ...