Bolts are externally threaded fasteners with metric or imperial (inch) screw threads with variety of thread profiles. Bolts are mostly used in combination with Nuts (Internally Threaded) with similar thread profile.
Since origin different types of bolts are developed with diversity in head styles, thread profile, etc.
On basis of Thread Profile, Bolts are classified into Metric Thread Bolts, Unified Thread Bolts, Acme Thread Bolts, Whitworth Thread Bolts and Buttress Thread Bolts. Further there are Metric Coarse Thread Bolts, Metric Fine Thread Bolts, Imperial Coarse Thread Bolts and Imperial Fine Thread Bolts.
Types of Bolts (Design)