Leash cup features concentric rings that create ledges to lock the leash cup into the board. Install the leash cup by drilling with a hole saw a hole slightly bigger than the diameter of the leash cup. Mix a small batch of putty with resin, cabosil, 3M bubbles or white pigment, and catalyst. Fill hole about 1/3 - 1/2 full with putty and insert cup. Clean off excess putty leaving putty slightly higher than the surface of the board so that as the resin cures and shrinks it will not shrink back below the level of the board. After the putty cures sand the putty and the cup level with the surface of the board.