goTUBE is designed with a 32mm OD in order to run in bearings and pillow blocks. The 16mm pattern is threaded into the ends of the tube so you can easily mount drive components to the tube for a no-slip transmission of power. The bore of the tube is both 14mm in diameter and a 12mm square. The 14mm diameter allows bearings to slide in the ends. The 12mm square bore caters to creating linear drives with lead screws.