The RAP-SB-224-2U is a 2.7 inch rubber suction cup base with twist lock and .75 inch inch diameter plastic ball. The suction cup base is designed to have an extra strong hold on any smooth non-porous surface, but for best results mount the suction cup base to a glass surface.
The RAP-SB-224-2U is commonly used with the RAP-SB-274-MFU (snap link ball and socket) or RAP-SB-275-FFLU (long snap link arm).