A bushing is required between the barbell and the socket to allow the socket to rotate under heavy weights. Bushings are low-friction materials placed between the bar and the sleeve, usually using copper bushings (sometimes composite) or needle bearings. Needle bearings rotate more smoothly than copper bushes (or some other bushings), but generally increase the cost of the rod. Both mechanisms produce sleeve rotation, but the bearings allow for smoother, quieter rotation and more reliable overturning at maximum loads. The standard Olympic barbell bar we produce, the selected needle roller bearings, and 4/8/10 different numbers of barbell rods, we can customize the barbell rods according to customer needs.