Introduction

Fasteners are used to assemble and hold machine parts. Fasteners may be threaded or nonthreaded: Threaded fasteners may be simple nuts and bolts or they may be complex holding devices; nonthreaded fasteners range from common rivets to complex latches. Fasteners may be general purpose or they may be special purpose; there are thousands of both types used in industry and most of them are readily available as catalog items. There are industry standards for all types of general purpose fasteners. Standards provide many advantages to manufacturers of fasteners; therefore, the manufacturers make their fasteners to conform to these standards. Because of this standardization, many dimensions for standard parts are not shown on drawings. As an example, a 1/4-in. socket head cap screw has a standard head diameter of 3/8 in. Tolerances for the head are 0.375 maximum and 0.365 minimum. Data of this type are not shown on regular assembly drawings. The nominal size of a fastener may or may not be the same as the actual size. As an example, a 5/16-in.-diameter bolt is 5/16 in. A 5/16 in. flat washer is designed to fit loosely over a 5/16 in. bolt. It has an inside diameter of 3/8 in., 1/16 in. larger than 5/16 in. It has an outside diameter of 7/8 in. Fasteners are generally made of steel, but they are also made of other metals including aluminum, brass, and titanium. Fasteners may be plated or plain. Plating may be with zinc, nickel, or some other material.