RAM Mount RAM® Tough-Mag™ 66MM Diameter Ball BaseRAM Tough Mag 66MM Diameter Ball Base Looking to mount to a metal surface? The RAM Tough Mag 66mm diameter base is the powerful and durable solution youve been searching for. With a B size ball screwed into a 20 threaded post, simply attach a compatible double socket arm and your desired RAM device holder. This base features an industrial strength N35 grade magnet and rubber coating that protects the metal surface youre attaching the RAM Tough Mag to.