Bolt and Fastener Chart: What's That Dingus Called?

That chart will be handy in my office so the raters can see what they are asking the importers about. BUT........ what is a cap screw?

Cap screw The term cap screw refers to many different things at different times and places. Currently, it most narrowly refers to a style of head (see the gallery below). More broadly, and more commonly, it refers to the group of screws: shoulder screws, hex heads, counter-sunk heads, button heads, and fillister heads. In the US, cap screws are defined by ASME B18.6.2 and ASME B18.3.^[21][22] In the past, the term cap screw, in general, referred to screws that were supposed to be used in applications where a nut was not used, however the characteristics that differentiated it from a bolt vary over time. In 1910, Anthony defined it as screw with a hex head that was thicker than a bolt head, but the distance across the flats was less than a bolt's.^[23] In 1913, Woolley and Meredith defined them like Anthony, but gave the following dimensions: hex head cap screws up to and including ⁷⁄₁₆ in have a head that is ³⁄₁₆ in larger than the shank diameter; screws greater than ¹⁄₂ in in diameter have a head that is ¹⁄₄ larger than the shank. Square head cap screws up to and including ³⁄₄ in have a head ¹⁄₈ in larger than the shank; screws larger than ³⁄₄ in have a head ¹⁄₄ in larger than the shank.^[24] In 1919, Dyke defined them as screws that are threaded all the way to the head.^[17]

A cap screw (narrow definition)

Cap screws (wide definition)

From Wiki.

Ohooo Kayyy ...... that is an interesting read and thanks for posting. Its an interesting hunt I'm on for the once and for all definition. Let me tell you why.

In the import business the customs tariff lists several types of screws, wood screw, machine screw, Drywall screw and cap screws ....... bolts are another story. When our clients (I'm the customs broker) imported screws and we asked them what kind? They usually just told us "normal screws, stop bothering me!" so we flipped a coin in the office and merrily went along our way. There was no difference in duty rates. Recently however it has been decided that China and Taiwan are "dumping" screws into our market and harming our domestic industry. Therefore a 170% duty rate was slapped on certain screws from China and Taiwan....EXCEPT for a few specific types. The most common among the exceptions is the "socket head cap screw". Now I can tell if it is a socket head just by looking, but what makes it a cap screw? Suddenly our clients seem to import nothing but cap screws, funny how that happens.

I think I'll stick with the ASME designations, if the screw doesn't meet those standards it isn't a cap screw.

Thanks again for your help.

A catalog such as this one is just as informative if not more so.