The #492 Step-Down Ring 49 - 40.5mm is a reliable and economical way to use filters. Using this ring saves you money since you won't have to buy the same filter two times for two different sized lenses. This 49 - 40.5mm Step-Down Ring allows you to use 40.5mm filters on lenses with a 49mm front filter thread size. A series of these reasonably-priced adapter rings is far less expensive than buying the same filter in two sizes. However, it should be noted that care must be taken when using Step-Down Rings in order to avoid vignetting. The rings are constructed of brass and feature a matte black finish.