Insert 2 rubber O rings (one at a time) inside the SMALL end of the coupling. Roll them down inside until they seat nicely up against a lip that is in there. This helps to seal the light around the top of the mag light and the coupling. You can see there is one down inside already.
Pkg of [email protected] 15/16" (ID) - 1 1/8" (OD) - 3/32" (Wall)
Molded Rubber O Rings = $.79