Blank or Screen-hinge.] The knuckle of the hinge is the cylindrical part that connects the two leaves, Fig.234.The "acorn" is the head of the "pintle" or pin that passes thru the knuckle.

Sizes of butts are indicated in inches for length, and as "narrow," "middle," "broad" and "desk" for width.
The pin may be either riveted into the knuckle as in box-hinges or removable as in door-butts.

Sometimes, as in blind-hinges, the pintle is fastened into one knuckle, but turns freely in the other.
A butt-hinge may be set in one of three positions, Fig.

235: (1) Where it is desired to have the hinge open as wide as possible, as in a door.

Here the knuckle is set well out from the wood.