The term “bolt” describes a threaded fastener with external threads that is made to be put together with a nut. The most common bolt head designs are the heavy hex, tap bolts (which is a fully threaded hex bolt), square head bolts, number three head plow bolts, and number seven head bucket tooth bolts. Hex bolts have hexagonal heads and machine threads to be used with a nut or in a tapped hole. Hex bolts are also known as hex cap screws or machine bolts.
Most screws and hex bolts are fastened in a clockwise direction. Drive screws are considered an inclined plane wrapped around a post. Screw sizes are based by the number. The higher the number, the thicker and wider the screw. Some screw threads are designed to meet up with a complementary thread, also known as an internal thread. The screw, nut and hex bolt industry is quite popular. The United States alone employs 118,998 people.
Early screws were made out of wood. They were used in olive oil presses, wine presses, and for pressing clothes. During the 15th century, metal screws first became available in order to connect objects together. Canadian, P.L. Robertson invented the square-drive screw in 1908. In the United States, the first handheld screwdriver was available in the 1800s. In the United States today there are approximately 4,031 nut, screw, and bolt manufacturers.