The SRFILTER comes prefabricated and ready to install in standard 48U rack enclosures on the inside of the door. Vertical Hook-and-Loop strips will need to be trimmed accordingly to accomodate 45U, 42U and 25U enclosures. When a filter becomes dirty or worn from use, be sure to replace. Hook-and-Loop pieces can remain attached to the door, with no need for replacement.