100% sterility guaranteed. These plastic Ultra-Dish petri dishes are packed in a double-sealed polyethylene sleeve to keep dishes sterile during transit, storage and handling. These heavy, clear dishes haveconsistently flat bottoms (never more than 0.005" off flat from edge to center). Flat dishes require less media for adequate coverage in the center of the dish. Stacking dishes feature a vertical stacking ring on lid to assure stable stacking. Designed for easy one-handed opening and closing. Edges are squared off to provide a firm, sure grip. The 716-2400 works well with FOSS units. Certificate of sterility is available upon request.