ISO Metric Screw Threads :
These threads are commonly used for general  fastening purpose. The most commonly used class of threads are 6H for internal threads and 6g for external threads.

Unified Inch Screw Threads ( UN and UNR Threads ) :
These threads are used for general fastening purpose and available as Unified Coarse thread series (UNC/UNRC), fine thread series (UNF/UNRF), extra-fine series (UNEF/UNREF).
The most commonly used classes of theads are 2A & 3A for external threads and 2B & 3B for internal threads.

These are parallel pipe threads having thread angle of 55° and are used where pressure-tight joints are not made on threads.

These threads have a taper of 1 in 16 and a thread angle of 55° and are used where pressure tight joints are made on threads.

These threads have a taper of 1 in 16 and a thread angle of 60°.  The types of threads include NPT, NPTF & ANPT.

Acme screw threads are mainly used for the purpose of  producing traversing motions on machines, tools etc.
The multi-start threads are used to provide fast relative traversing motion.

The Stub Acme screw threads are generally confined to those unusual applications like transmission of power and motion where a  coarse pitch thread of shallow depth is required due to mechanical or metallurgical considerations.

Trapezoidal threads are used for transmission of power and motion and are nearly similar to ACME threads, but are made to metric dimensions and standards.

The most commonly used class of threads are 7e for external threads & 7H for internal threads.

These are asymmetrical threads and are used for transmission of power in one direction. The most common thread profile is 7° / 45°.

Round Threads :
These threads are also known as Knuckle threads and are insensitive to dirt and damage due to their round shape and are used in fastening screw threads in clutch of railway cars and for large valves and gates, for bottle caps etc.