PSA is only recommended when it is completely necessary. Once the film is stuck to the surface it cant be removed & reused. This creates a potential & likely problem of debris adhering to the film that cannot be removed. Any debris that comes in contact w/ the fiber may cause a scratch. The 2″ disk is the standard size for the Ultra Tec Minipol-2 and UT-9005 series, but they do not require PSA or a center hole.