The screwdriver is threaded into square metal part. The piece is heavy, but not used as a hammer. The handle is loosely held between the thumb and index finger and bounced along the edge of the fint: the weight of the tool does the work, and the edge of the square makes nice small chips on the edge of the flint. The screw driver is used to tighten the jaw screw, and is not used to knap the flint. This tool was made in 1970. I am the second user and have used it the past 30 years, and have found nothing better. I hope you make one to use: you will like it.