Zip Box 138mm Round holds one 138mm filter or diopter and clamps on the front of a lens. Available in four sizes 80-85mm, 90-95mm, 100-105mm, and 110-115mm. Due to the open front of the Zip Box, it can hold a diopter of any strength. The lens shade design allows for even the widest lenses and sensor sizes to be covered without vignetting. Zip Box is extremely lightweight and weighs about the same as a standard filter which makes it perfect for gimbal and drone use. Stainless steel components and unibody rubber design are very durable and stand up to the toughest conditions. It is important to note that you should measure based on outside lens diameter and not based on the threaded filter ring size.