... because they produce cutting that are easiest to log. Usually 2-wings drag bit, 3-wings drag bit, 4-wings drag ... optional. Shapes can do chevron & step as requested. Sizes: 3 3/4", 3.7/8", 4", 41/4", 55/8 ", 47/8 ... /8" 7.3/8" 9.7/8",11.1/2" etc as requested. Our standard type already exported to USA, Australia ... any interests and need more information, Please feel free to contact 3 blades API drag bit