Shoulder screws are a type of machine screw or tapping screw with integral threads that are only present on half or less of the screw shank. A shoulder screw has a partially smooth shaft that will allow the bolted material some rotation and movement around the screw axis. Shoulder screws with machine screw threads will require a predrilled head and is often threaded into a nut while self tapping shoulder screws remove the steps of pre-drilling and tapping.