OM System PRLC-14 Underwater Housing Lens Cap

The front port of an underwater housing is the part that scratches, and it scratches in the bag between dives rather than in the water. The PRLC-14 caps it, so the flat optical face arrives at the boat in the same condition it left the shop.

It fits the PT-053, PT-055, PT-056, PT-058 and PT-059 housings. Buy a second one if you shoot two bodies; a scratched port is not a cleanable fault.