Classification of screws

The main categories include ordinary screws, machine screws, self-tapping screws and expansion screws.
Cap screw used to be limited to full-tooth fasteners.
Hexagon head screw Hex cap screw and large hexagon bolt Hex bolt, as the name suggests, are externally threaded fasteners with hexagon head, designed to be turned with a wrench. According to ASME B18.2.1 standard, the tolerance of head height and rod length of hex cap screw is smaller than that of general hex bolt. Therefore, ASME B18.2.1 hex cap screw is suitable for installing in the place where all hex bolts can be used, including the place where the big hex bolt is too large to be used.
Socket cap screw (also known as socket head screw or socket head screw) is a screw with a hexagon internal hole on the head. It can be tightened or loosened only after the hexagon key, Allen wrench or Allen key is inserted into the internal hole. The most commonly used hexagon socket head screws are cylindrical head screws, with the head diameter about 1.5 times of the main diameter of the thread (1960 series). Other head types include the bottom head cap screw which makes the surface beautiful and the countersink head cap screw which is suitable for the conical screw hole. The counterbore design allows the screw head to rotate without being exposed to the surface of the fixed object, so it is often used in places where the surface is small and the traditional wrench is inconvenient to use.
Generally speaking, the diameter of machine screw is less than¼ Inch screw (4 #~12 #), usually full tooth and rotated by a screwdriver, such as slotted, cross or hexagonal socket.