14.1 Bolts, Screws, Nuts, and Washers

Bolts and screws are the most commonly used types of fastening devices. The thread on a bolt or screw may be compared with an inclined plane wrapped around a cylinder, thus assuming the form of one of the basic machines. Many different thread-form standards are used throughout the world, but this chapter addresses only the forms in common use, such as the 60 V thread form for the U.S. Customary (inch) system and the metric [International Standards Organization (ISO)] standard. The other basic thread forms and their geometry are shown in Chap. 7, "Machining, Machine Tools, and Practices."

14.1.1 Dimensions of Bolts, Screws, Nuts, and Washers

Basic dimensions for the most commonly used American standard bolts are shown in Fig. 14.1. Basic dimensions for the most commonly used American standard machine screws are shown in Fig. 14.2. Basic dimensions for American standard miniature screws are shown in Fig. 14.3.

	Hex Bolts	Hex Cap Screw (Finished Hex Bolts)	Round Head Square Neck Bolts	Countersunk Bolts
Nominal size
Basic Dia.	d	F	P	h	d	F	P	h	D	F	h	k	d	D	h	W [?]
0.2500 - 1/4	0.260	0.438	0.505	0.188	0.2500	0.438	0.505	0.163	0.594	0.260	0.145	0.156	0.260	0.493	0.150	0.064
0.3125 - 5/16	0.324	0.500	0.577	0.235	0.3125	0.500	0.577	0.211	0.719	0.324	0.176	0.187	0.324	0.618	0.189	0.072
0.3750 - 3/8	0.388	0.562	0.650	0.268	0.3750	0.562	0.660	0.243	0.844	0.388	0.208	0.219	0.388	0.740	0.225	0.081
0.4375...