The E-10 flip 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.
The E-10 fits all Vortex® Riflescopes except the 1-inch / 25.4mm tube Viper® model VPR-M-01BDC, VPR-M-04BDC and VPR-M-03BDC.
Outer diameter: 40-46mm