TABLE OF CONTENTS Bolts, screws, and nuts are the most commonly used types of fastening devices. The thread on a bolt or screw may be compared to an inclined plane wrapped around a cylinder, thus assuming the form of one of the basic machines. Many different thread form standards are used worldwide, but this section will present data pertaining only to the forms in common use such as the 60 V-thread form for the U.S. customary (inch) system and the metric (ISO) standard. The other important thread forms used worldwide and their geometry are shown in Sec. 10.2.
Threaded fasteners have countless applications in industry, and in many cases their performance is critical. Failure of a threaded fastener such as a heavily loaded bolt or bolts can cause severe injury, property damage, and death in critical applications. It is for these reasons that standards of performance have been devised and specified in the various American standards such as ANSI, ASTM, SAE, and Industrial Fasteners Institute (IFI). In recent years, it has been nationally discovered that counterfeit bolts are being imported into the United States. False head markings and inferior steels have been found, which have contributed to many failures in critical applications. Figure 10.1 shows a typical counterfeit bolt that failed during the installation process. This is a direct indication of improperly processed material or poor-quality material. Other cases have been cited where the failure was through the threaded section and also cracking due to improper...
