. These fasteners are designed to drill their own pilot hole, form a mating thread, and complete the fastening in a single operation, eliminating the need for pre-drilling in metal substrates Bugel Алматы Core Technical Specifications According to the DIN 7504 Standard , the "K" designation specifically refers to the Hexagon Head with Washer/Collar Specification Details Common Diameters ST3.5, ST3.9, ST4.2, ST4.8, ST5.5, ST6.3 Dega Demir ve Galvaniz Sanayi A.Ş. Head Style External hexagon with a fixed flange (collar)