Vortex Optics Defender Scope Eyepiece and Objective Lens Cover - E-10 p This is the last flip cap you will ever need. Virtually indestructible, this cap will fit snugly on nearly all Vortex Optics and features a snap flat spring that will keep your line of sight unobstructed. The E-10 cap is has three stop positions. The first vertical, to put your dope disk (optional accessory) literally right in your face. The second at a 45 and the third at 90 to lay flat back. Outside diameter: 40-46 mm | 1.57-1.81 inches. Objective Lens Cap: O-24, 28-31mm.