Larger drain upgrade for MR-1 CNC. Designed to fit Oatey Designline 4 in. x 4 in. Stainless Steel Square Shower Drain with Square Pattern Drain Cover from Home Depot. Must be installed before concrete is poured. Rubber is Multipurpose Neoprene Rubber Sheet 1/8" 50A hardness 12"x12" sheet. Bolts are ¼-20 X 1.25" SS.