This Warren-Knight WK-58-9005 Ball Holder is a cup mount for spherical adapters or targets. Used for any sphere with a 3½” diameter sphere. The W-K Ball Holder is made of stainless steel. It has a 2″ height and a 1¾” radius with an adjustable height of ¾”. The vehicle column of the holder is hollow to permit downward sighting through it. The WK-58-9005 has threads of 1¼” x 7 UNC. It meets AIA specifications.