Impact screwdriver comes in a set. Usually a 3/8" drive to 5/16" screwdriver bit size. You put the bit end in the screw, & while twisting & holding pressure on the body of the tool in the direction you want the bit to turn, you strike it end with a BFH. Works on the same principle as a pneumatic impact, except you supply the torque, instead of air. It'll still break bits, screws, bolts, etc.. But you can control the amount of torque by how hard you strike the tool. Use lots of Kroil (lol) before you strike it.