Pan heads are slightly rounded with short vertical sides. Machine screws have machine threads for use with a nut or in a tapped hole. 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. 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.