The RFM18 Universal Tower Flat Roof Mounting Base, made of regular steel, attaches a UT20 or UT30 tower to a flat surface via user-supplied anchors. It requires the UTGUY Tower Guy Kit. The mounting holes in the RFM18 were 1/2 inch diameter, but were changed to 5/8 inch diameter to fit our standard j-bolts. Note: Campbell Scientific does not recommend using the RFM18 in marine environments unless the user paints a rubberized coating on it or takes some other preventive measure to insulate the metal from the air.