Thomas

Bolts and screws are quite different, although they do the same job of keeping two or more things together. Both have threads, but the threads of screws tend to be much more aggressive than those of bolts of the same dimensions. There is a reason for this.

A bolt is usually used with a nut and one or two washers. The purpose of the nut is to tighten or loosen the bolt, and that of the washer is to increase the area under pressure, thus reducing the chance of damage to the pieces being held together. The tip of the bolt is usually flat or nearly so. A washer is placed over the bolt and pushed up the head. The bolt is then pushed through existing (pre-drilled) holes in the two objects to be joined. A washer is added and then the nut. (bolt + washer + first object + second object + washer + nut) To loosen or tighten the bolt, if it has a nut, you turn the nut and not the bolt. As you turn the nut, it travels up or down the bolt along its threads in accordance to the direction in which you are turning it. Note that to turn the nut, you use a wrench. The wheels of a car are held on by means of bolts that are attached permanently to the car. No washers are used, but from five to six nuts are per wheel are.

Screws can be used with or without washers. Screws do not have nuts. Their aggressive threads create threads in the metal or wood they are penetrating. The tip of the screw is conical to permit it to bore its way though soft metals and wood. Screws are turned by a screwdriver. Of you look at the hinges on your door, without doubt they are held in place by large screws, not bolts.