The machine screw is a smaller diameter bolt and comes in several different head styles. These screws have flat ends and use a nut to complete the fastening. The machine screw is used in mechanical construction and product assembly such as machinery, appliances and electronic panels. Machine screw head styles include round, pan, flat and flat undercut. Drive types are phillips, slotted and phillips/slot combo. Each screw style allows the screw to be flush against the surface when fastened.