The RAM Yoke Clamp Base with 1' Rubber Ball and 1/4-20' Tap from RAM MOUNTS includes a 1/4-20' thread in the back side of the 1' ball. The clamp fits a rail diameter from 0.625' to a maximum of 1.25'. The 1' rubber ball is at a right angle to the plane of the mount so when connected to a rail, the ball sits parallel to the rail.