head jamb

There are approximately 3 inches at the side jambs and 11/2 inches at the head jamb for fitting purposes.

The horizontal jamb, called the head jamb, across the top of the doorway is usually fastened into grooves in the side jambs.

When framed in wood for snug fitting of a door, the doorway consists of two vertical jambs on either side, a lintel or head jamb at the top, and perhaps a threshold at the bottom.