Description ***View our Size Chart to find your best fit.*** The OnGlass Spacer OG 2.0/3.0 is the interchangeable piece that matches your OnGlass system to a specific spotting scope or binocular eyepiece. Each spacer snaps into the adapter ring without tools and holds the optic in the correct position for repeatable MagTab alignment. Available in eight sizes, it&&';;s an easy way to add a second optic to your setup or keep a spare ready for quick changes in the field. Sizing Size Eyepiece Diameter Measurement Alpha 1.55 - 1.64" Bravo 1.65 - 1.74" Charlie 1.75 - 1.84" Delta 1.85 - 1.94" Echo 1.95 - 2.04" Foxtrot 2.05 - 2.14" Gulf 2.15 - 2.24" Hotel 2.25 - 2.34" How to measure: To measure your spotting scope or optic eyepiece, place a tape measure across the widest point of the outer eyepiece housing. Measure straight across the center from one outside edge to the other to determine the eyepiece diameter. Specs Includes 1 optic spacer Manufacturer Warranty Lifetime against manufacturer defects