Trijicon RMR compatible sealing plate manufactured by Maple Leaf Firearms.
Required for use with electronic RMRs (Auto Adjusting LED and Adjustable LED), and recommended for use will all RMR models to guarantee waterproofness on mounting surfaces that do not completely cover the o-ring on the bottom of the optic.
With the sealing plate installed properly between the RMR optic and the mounting surface, the RMR can be submerged up to 66 feet, for at least one hour without leakage.
Made from stainless steel. Weighs 2.8 grams.
I feel it is a mandatory piece of equipment for running a RMR. For the cost of the sealing plate it is cheap insurance to ensure proper function of a Trijicon RMR.