CB-50D is designed especially for our tournament class tripod. By attaching CB-50D, our new tripod leg tubes will not touch the ballhead knobs at its' reverse folding position. The sphere and the base plate of CB-50D are controlled by individual locking mechanisms. CB-50HN locks both its' sphere and base plate by a main knob, but adding a sphere control knob to lock the sphere alone and the plate rotates freely.