This is a 50A 125/250V shore power inlet, most frequently mounted in the boat's cabin side or cockpit coaming.

Gasketed, self-closing cover so the interior is shielded from the elements when not in use
Watertight when the cover is securely fastened
Mounting holes are 2-3/8" on center
Rear portion has a 2.171" diameter
Mounting screws and gasket are included


Heavy on the technical side...

There are two categories of 50 Amp devices: 50A 125V (50A 3-wire), and 50A 125/250V (50A 4-wire).
The 3-wire devices have a single "hot" leg carrying 50A 125V.
The 4-wire devices have two "hot" legs, each carrying 50A 125V. (50A 250V when combined.)
These two categories are NOT interchangeable.
Never alter the plug of one type of these devices to fit into the receptacle or female connector of the other type.