Metal covers for Precision bass bridges. These were typically installed over the bridge unit vintage style Precision basses. They provide an additional surface for a player to rest their hand on - giving the bass an entirely new feel and playability.
Newer models of Precision basses typically omit the cover, but there are still some players who enjoy the look and feel, nevertheless!
Length (at longest): 116mm
Width (at widest): 67mm
Height (at highest): 21mm
Mounting hole distance: 121.5mm