The optech usa hood hat medium is designed to fit a lens and shade with a diameter from approximately 35 40 simply placing the hood hat onto the front of the hood while in place will provide just as much protection for the critical front lens elements as would be provided by a traditional lens cap the neoprene material will adjust to fit both round and elliptical petal type shades this item is made in the usa neoprene stretches for a custom fit on round or elliptical petal t