The E-10 cap 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: 41.5-46 mm | 1.6-1.8 inches
The E-10 fits all Vortex® Riflescopes except the 1-inch tube Viper® model VPR-M-01BDC, VPR-M-04BDC and VPR-M-03BDC.
Note: Image shows dope disk that is NOT included.