Monstrum Pro Series Scope Lens Covers help you keep your glass clean and damage free for when you need it most. Rubberized sleeves are crafted from an improved rubber formulation - designed to fit snug around your scope tube with more resiliency than ever before. Spring loaded flip-up lens caps deploy with the flick of a thumb and secure tightly when not in use. Each package includes one Flip-Up Lens Cover. For optimum fit, carefully measure the diameter of both your rifle scope's eyepiece diameter and objective lens diameter and choose the size from the chart below. Example: if your eyepiece measures 31mm, then you should order Size C so it fits tighter.