What is the difference between a bolt and a screw?
Historically the difference between a bolt and a screw was that the screw was threaded to the head whereas the bolt had a plain shank. However I would say that now this could cause you a problem if you made this assumption when specifying a fastener. The definition used by the Industrial Fastener Institute (IFI) is that screws are used with tapped holes and bolts are used with nuts.Obviously a standard ‘bolt’ can be used in a tapped hole or with a nut. The IFI maintain that since this type of fastener is normally used with a nut then it is a bolt. Certain short length bolts are threaded to the head – they are still bolts if the main usage is with nuts. Screws are fastener products such as wood screws, lag screws and the various types of tapping screws. The IFI terminology and definition has been adopted by ASME and ANSI.
This is a question that engineer’s have argued for years, and continue to disagree on to this day. We have yet to see an all inclusive answer. The oldest argument has been a bolt takes a nut and a screw does not. This obviously does not take into consideration that most all bolts are classified as Hex Head Cap “Screws” by all major fastener governing associations.
