Alcatraz Island - Golden Gate National Recreation Area
Photo -- See Caption Below

Locking mechanism for a gate or sally port door. This kind of lock would have been used in a doorway between sections of the prison, such as, between the cellhouse and the yard, or between the mess hall and the kitchen. It would not have been used in a door to an individual prison cell.
Brass, ferrous metal. L 15.3, W 9.6, T 5.2 cm
Golden Gate National Recreation Area, GOGA 9927