The RAM-B-108B-STRAP40U accommodates rails from 2" to a maximum of 3" in diameter. To mount the RAM-B-108B-STRAP40U base, place the saddle shaped plate on the rail then wrap the metal clamp strap around the rail and plate. Tighten the screw knob on the metal strap with a screwdriver until the strap has a firm hold on the rail. The RAM-B-108B-STRAP40U is an alternative mounting base for aircraft such as the Bonanza or Beech with a “throw over yoke”.