Thread Diameter 0.250" Head Diameter 0.477" Head Height 0.153" Machine screws are often used with nuts but also often driven into tapped holes (without nuts). They might be considered a screw or a bolt based on the Machinery's Handbook distinction. In practice, they tend to be mostly available in smaller sizes and the smaller sizes are referred to as screws or less ambiguously as machine screws, although some kinds of machine screw can be referred to as stove bolts. A flat head is A head with flat top and a conical bearing surface (bottom). Designed to be Countersunk. Rod with spiral threads the entire length and with one flat end and a head on other end. Holds object to another object that has a pre-threaded hole, frequently a nut. Usually manufactured from metal. Can be rotated into or out of the object using a screwdriver or wrench.