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For the secondary mirror, the standard back plate for the collimation screws on most Dobsonian telescopes is metal. The collimating screws press against this plate to move it during collimation and to hold it in place. Over time the metal plate is often gouged by the screws, creating divots that hinder the accuracy of collimation. The UHMW-PE Washers sit on top of the metal plate and, with a high resistance to wear-and-tear, prevent these divots ensuring higher accuracy of collimation even after years of use.