The Legendary Butler Creek flip-up caps spring up with the touch of your thumb. It features a tight, flexible collar provides custom fit for multiple scopes, sealing out dust and moisture. The ocular lens covers feature a large push button for quick spring loaded opening when you want to keep your optics protected until ready for use. To select the correct cover, refer to the scope’s owners manual or measure the outside diameter with calipers and select the closest measurement from the table below.. Same basic features of standard Flip-open Covers. . Very quiet & durable.