Heavy Duty Base Plates designed for heavy and more commercial style green houses, They are sold individually,so you only buy the amount needed for your greenouse.. Safely secures your ClearSpan building (Greenhouse) or canopy to any wood or concrete surface!Heavy Duty Base Plates can be used on all surfaces.4" x 5-1/2" plates have 4 pre-drilled 1/2" fastening holes.Can accommodate two pipe sizes(1.315"/1.660" OD pipe,1.315"/1.660" OD pipe.