Our lens caps are the standard spring fit lens caps that clip into the filter thread of your lens. If you are not sure what size you need, look at the front of your lens. Many lenses have the filter thread size marked on them. For example, a lens with a 58mm filter thread will be marked "Ø58mm" and will therefore require a 58mm lens cap. If your lens is not marked, consult your user manual. As a last resort, measure across the front of your lens directly between the threads. Please contact us if you require assistance.