Or a bolt. And, often, nuts. The full page has many more illustrations and examples.
Reshared post from +Guy Kawasaki
Total guide to screwing. See the whole chart here:
http://www.boltdepot.com/fastener-information/Type-Chart.aspx
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Nut Screws Washers and Bolts.
— Supposedly an old UK Sun headline
I made a chart similar (and more specialized) than this for new technicians and customers at the computer store chain I once worked at. But I have mechanical reference books that include charts that make this one look simplistic. Most people are simply unaware of the depth of standards that make up their manufactured environment. Once upon a time, high schools taught mechanical arts classes, and some of the better ones were quite advanced. That's almost all gone now. /rant https://picasaweb.google.com/lh/photo/QcQ_CI-bZjclPhRhbwysxdMTjNZETYmyPJy0liipFm0?feat=directlink