The narrow stainless steel bar at the back is only 2.6 mm in diameter, preventing tuberosity impingement, while still giving it rigidity equal or better than any other disposable Posterior dual arch tray. The Harmony Posterior Tray narrows to the back of the mouth, and the side walls are low. Other trays stay the same width, and even become larger in places towards the back of the mouth. This is the cause of tuberosity impingement and poor bite registration. The steel bar in the Harmony Posterior Tray offers superior rigidity, which is a large factor avoiding distortion of the impression.