Among the commonly used fasteners to keep the parts of machines together are screws and bolts.  There are different types of screws and bolts.  They vary on heads, threads, and more.  Bolts and screw are confused by amateurs many times.  However, they are different types of fasteners. A Bolt is a headed fastener with an external thread to use for non-tapered nut.  A bolt requires a nut as counter to lock the joint.  Bolts have uniform threads to satisfy the standard of the specifications like MJ, UNR, UNJ and others.  They are used in most applications in industries.  Bolts are designed to be used as fasteners that are placed through holes that are already drilled in parts of machines.  These bolts require nuts to tighten it.

Screws on the other hand are externally headed threaded fastener type.  Screws don’t have to meet some specification standards unlike bolts.  They’re shaft with provision in one end for turning the screw.  They have a helical thread on their surface capable of piercing into the surface.  They don’t require nut unlike bolts and they are mostly used in applications that are home-based.