4.75mm ball and ball-link are the most common combination in 400 class market, while 3.5mm ball and ball-link dominates the 300 class market. Smaller size of ball has less angle of joint due to the screw size cannot be too small. For bigger size, it is a kind of overhead that it need a larger gap and space for the large ball-link to move freely. Explanation of 4mm Ball Link Advantage In our design, we get a balance point that choosing 4mm ball-link with small stem to ensure have at least 30 degree angle of joint.