What is a Hinge Joint (and the other parts of a butt hinge)?

Hinges

This hinge has 2 “caps”, 2 “leaves” and 5 “knuckles”.  The 5 knuckles make up the hinge “barrel”.  Inside the hinge barrel is the hinge “pin”.  A hinge does its job by pivoting around the hinge pin.  The hinge barrel and the hinge pin comprise the hinge “joint”.  The hinge joint is the pivoting mechanism of a hinge, just like your elbow joint is a pivoting mechanism for your arm.

To measure a hinge joint, measure from top to bottom and don’t include the caps.