B Size / M8x1.25x8mm Male Thread: The RAM Mounts Tough-Ball Ball Adapter (RAP-B-379U-M81208) consists of a 1" diameter rubber ball, connected to a M8-1.25 X 8MM male threaded post. Features: Thread pitch: M8-1.25 x 8 mm. Material: High-strength composite with stainless steel threads. Ball size: 1" rubber ball "B" size. B Size / 1/4in-20 x 1/4in Male Thread: The RAM Mounts Tough-Ball Ball Adapter (RAP-B-379U-252025) consists of a 1" diameter rubber ball connected to a 1/4"-20 x 0.25" male threaded post. The male thread matches most standard camera and camcorder female threads found on the bottom of these devices. Features: Thread pitch: 1/4"-20 x 0.25". Material: High-strength composite with stainless steel threads.