Solid shelves are a solution where dirt, dust and spills are a potential issue. The solid flat surface allows for storage from small to large items and the marine edge perimeter prevents spillage. The double hemmed 18 gauge 304 stainless steel gives the solid shelf excellent strength characteristics. Add-on kit allows you to expand your starter kit by sharing a set of posts. Configuration options include straight line, back to back and right angles (L-Shape). Add-on unit consists of 4 shelves, 2 posts and 10 shelf clamps. Additional shelves may be purchased separately. Units with add-on kits cannot be made mobile.