The devices used for holding together two parts of a machine or a structure are called fasteners. Fasteners are divided into two main categories: temporary fasteners and permanent fasteners. Temporary fasteners allow easy unfastening of the parts connected, without damaging the fastening elements, while with permanent fasteners, the parts when joined once cannot be separated without breaking the joining element. Nuts, bolts, screws, studs, keys, cotters and pins, etc. are examples of temporary fasteners. Riveting, welding, soldering brazing, etc., provide permanent fastening.Â
Threaded Fasteners:Â
Threaded fasteners may be classified into three groups: bolts and nuts, studs, and set screws.
Bolts have a solid head at one end and are fitted with a thread at the other on which a washer and nut are placed to secure it. Bolts are made with a variety of head shapes to suit the position in which they are to be used. The important types of bolts are hexagonal bolts, square-headed bolts, cup or round-headed bolts, cylindrical or cheese-headed bolts, T-headed bolts, eye bolts, hook bolts, and counter sunk-headed bolts.