The U.S. Customs and Border Protection issued An Informed Compliance Publication, March 2006,
What Every Member of the Trade Community Should Know About: Distinguishing Bolts from Screws, which states…
U.S. Customs and Border Protection uses fastener industry standards to distinguish bolts from screws. When a fastener is described in a fastener industry dimensional standard as either a screw or a bolt, we follow that standard. When we have no dimensional standard, we go to "
Specification for Identification of Bolts and Screws," ANSI - ASME B18.2.1 1981 (the "
specification"). In
Rocknel Fastener, Inc. v. United States, Slip Op. 00-112 (Ct. Int'l Trade, decided August 29, 2000), the court sanctioned ANSI/ASME Standard B18.2.1 as "provid[ing] a well-recognized, comprehensive basis for the common and commercial meaning of bolt and screw as understood by the fastener industry in the United States."
Since the
United States Court of International Traderecognizes ANSI - ASME B18.2.1 1981 as "provid[ing] a well-recognized, comprehensive basis for the common and commercial meaning of bolt and screw as understood by the fastener industry in the United States," we can describe bolts and screws thusly…
A
bolt is a fastener that has external threads (a nut, for example, has internal threads), is inserted into an unthreaded hole of one or more parts, and is tightened or loosened by turning its nut. Carriage bolts, elevator bolts and plow bolts, for example, are bolts because you can't turn their heads to tighten or loosen them.
A
screw has external threads just like a bolt. But a screw is inserted into a threaded or unthreaded hole, and is tightened or loosened by turning its head. It may or may not be used with a nut. Wood screws and sheet metal screws make their own threads in the hole, so they are not used with a nut. Machine screws and cap screws, for instance, thread into threaded holes or are used with a nut. In either case, though, you tighten or loosen the screw by turning its head.
With regard to Hex Bolts and Hex Cap Screws it is commonly accepted that it's a Hex Cap Screw if it has a washer face bearing surface and if it doesn't it's a Hex Bolt. That belief is supported by ASME Standard B18.2.1.
Naturally there are exceptions to every rule as the
Millwrights and Mechanics Guide 4th Edition observes: "These definitions obviously do not always apply, since bolts can be screwed into threaded holes and screws can be used with a nut." And several other examples come to mind: A toggle bolt consists of toggle wings, which is a special spring-loaded collapsible nut, and a screw—you always tighten the screw, but the assembly is called a toggle bolt. Stove bolts are machine screws supplied with machine screw hex nuts. Lag screws are sometimes called lag bolts. And fully-threaded cap screws are also called tap bolts.
Most of the fasteners at
Fastener Mart follow the bolt/screw rule. But even if they don't, we've worked hard to make it easy for you to find what you're looking for.
And of course now that the United States Court of International Trade has ruled, we suppose the question is: Has the bolt/screw debate finally been put to rest?