These donut lids are key part of our pint-sized BugDorms. They can cover petri dishes (NOT sold) with external diameters of 89 mm or less. These donut lids may also fit onto your own cups if mouth diameters are the same. The donut lid has a matt surface for retaining penciled notes. Its 104 x 94 mesh Nylon screen, if stained, can be replaced with clean Nylon mesh circles (sold separately) or with your own screen materials. Circles of 150 x 150 mesh Nylon screen are also available (sold separately) to effectively keep aphids, thrips, and parasitic wasps from escaping the cup. Stockinet sleeves for the pint-sized BugDorm can be purchased separately if you do not wish to remove the lid to access cup interior.