Yes they are both externally threaded fasteners, but how can you tell the difference?

Bolt- torque the nut

Bolt-externally threaded fastener that is

  • designed for insertion through holes in assembled parts
  • normally intended to be tightened (or released!) by torquing a nut

Screw- Torque is applied through the head...

Screw-externally threaded fastener that is capable of

  • being inserted into holes in assembled parts;
  • mating with a preformed internal thread, or forming its own thread;
  • being tightened or released by torquing the head.

A bolt is designed for assembly with a nut.


Nuts are required for bolts, optional for screws.

A screw has features in its design which makes it capable of being used in a tapped or preformed hole in the work. Because of basic design, it is possible to use certain types of screws in combination with a nut. Any externally threaded fastener which has the majority of the design characteristics which assist its proper use in a tapped or other preformed hole is a screw, regardless of how it is used in its service application.

Source: Distinguishing Bolts from Screws, US Department of Homeland Security, March 2006.