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629C H A P T E RN I N E T E E NFASTENERSThe Big PictureYou Are the Designer19–1 Objectives of This Chapter19–2 Bolt Materials and Strength19–3 Thread Designations and Stress Area19–4 Clamping Load and Tightening of Bolted Joints19–5 Externally Applied Force on a Bolted Joint19–6 Thread Stripping Strength19–7 Other Types of Fasteners and Accessories19–8 Other Means of Fastening and JoiningDiscussion Map■ Fastenersconnect or join two or more components. Common types are boltsand screwssuch as those illustrated in Figures 19–1 through 19–4.THE BIG PICTUREFastenersIn this chapter, you will learn to analyze the performance of fasteners and to select suitable types and sizes.DiscoverLook for examples of bolts and screws. List how many types you have found. For what functions were they being used? What kinds of forces are the fasteners subjected to? What materials are used for the fasteners?A fasteneris any device used to connect or join two or more components. Literally hundreds of fastener types and variations are available. The most common are threaded fasteners referred to by many names, among them bolts, screws, nuts, studs, lag screws, and set screws.A boltis a threaded fastener designed to pass through holes in the mating members and to be secured by tight-ening a nut from the end opposite the head of the bolt. See Figure 19–1(a), called a hex head bolt. Several other types of bolts are shown in Figure 19–2.(a)(b)FIGURE 19–1 Comparison of a bolt with a screw (Reference 9)FIGURE 19–2 Bolt styles. See also the hex head bolt in Figure 19–1 (Reference 9)
630PART THREEDesign Details and Other Machine ElementsA screwis a threaded fastener designed to be inserted through a hole in one member to be joined and into a threaded hole in the mating member. See Figure 19–1(b). The threaded hole may have been preformed, for exam-ple, by tapping, or it may be formed by the screw itself as it is forced into the material. Machine screws, also called cap screws, are precision fasteners with straight-threaded bodies that are turned into tapped holes (see Figure 19–3). A popular type of machine screw is the socket head cap screw. The usual configuration, shown in Figure 19–3(f), has a cylindrical head with a recessed hex socket. Also readily available are flat head styles for countersinking to produce a flush surface, button head styles for a low pro-file appearance, and shoulder screws providing a preci-sion bearing surface for location or pivoting. See Internet sites 9 and 11. Sheet-metal screws, lag screws, self-tapping screws, and wood screwsusually form their own threads. Figure 19–4 shows a few styles.Search for examples where the kinds of fasteners illustrated in Figures 19–1 through 19–4 are used. How many can you find? Make a list using the names for the fasteners in the figures. Describe the application. What function is the fastener performing? What kinds of forces are exerted on each fastener during service? How large is the fastener? Measure as many dimensions as you can.