Types of screws: the answer is five. Self-tapping screws:Self-tapping screws are pointed, coarse teeth, hard texture of wood screws, but also aluminum alloy, plastic, for tapping metal holes threaded a special self-tapping screws are called taps.1, ordinary screws: is the use of the friction of the object inclined circumference of the rotation of the object to tighten the object and the parts of the tool gradually.2, self-tapping screws: refers to the texture of the hard, coarse teeth, pointed wood screws, but also refers to the aluminum-plastic alloy. Used for tapping metal holes in the special self-tapping screws called taps. 3, expansion screws: known as metal expansion bolts, expansion bolts fixed using a wedge-shaped beveled to promote expansion, resulting in friction bonding force, to achieve the fixed effect.