Fig 342 Incand Nav Light Bulb - 24V DC, 55W, Med Prefocus

These clear, incandescent, medium prefocus bulbs are used in navigation fixtures on vessels over 65.6 ft (20m) in length.

Prefocus bulbs have bases which ensure that the bulb filament (or LED light source) is in a specific orientation with respect to the light fixture's lens when seated in the socket.
This is a common requirement for certain vehicle and navigation lights. Prefocus sockets come in several sizes such as Medium and Mogul.

This bulb is used on boats wired for 24V DC and these Perko fixtures:
Figs. 1150-1154 all-round red lights on vessels from 20m-50m, as well as the port, starboard, white masthead, and green all-round lights on vessels >20m
Figs. 1369-1374 black plastic single lens lights
Figs. 1364-1368 black plastic double lens lights
Figs. 1169-1174 bronze single lens lights
Figs. 1164-1168 bronze double lens lights
Figs. 1111, 0403, 0412, 0454 specialty lights