Ruff's Precision Manufacturing meticulously designs its products to be compact and lightweight while being compatible with as many optic/accessory combinations as possible.This rail cap accessory allows you to add both rail mounted laser rangefinders or secondary aiming devices (red dots) to your magnified optic.This is a simple cap replacement that fits ALL existing RPM products (CLR series rings and all Bravo/Delta cantilevers). The cap screws included in the original purchase are the exact screws needed to install this accessory.