What is the Difference Between a Bolt, a Screw and a Stud?

posted in: Thoughts | 0

We as engineers get hung up on technical arguments that are not technical at all.

Bolts, screws and studs, what’s the cutoff where one stops being a screw and becomes a bolt? It’s more a matter of their function, rather than an arbitrary size or if a there is HEX head on one end. Screws usually go into a blind hole or sheet metal. Screws have self-cutting threads designed to cut female threads in the mating parts. The word “bolt” sounds strong, thus people tend to think of some grand size differentiating a bolt from a screw.

A bolt is designed for use with an already threaded part, such as a nut or a female tapped hole. Unlike a screw, generally speaking, a bolt is used to go through the parts and be secured with a nut on the opposite end from the HEX.

A stud is a threaded rod, nothing more. It may have a slot or cross for a flat or philips screwdriver, respectively. Studs are specifically designed to go through a length of sandwiched parts, like a flange to flange long pipe with gaskets in-between. Take a look at a flow indicator for example: Full View Flanged Flow Indicators

All this fascinating discussion what defines what is inherent to us engineers. When confused, use “threaded fasteners” instead and make a better world. Still confused? Take a look at what the gold standard McMaster has to say about it. McMaster-Carr. So, there, use screws, bolts or studs for your designs as best optimized and call it whatever you want.