This size 2 PROGAF filter bag has a specially deloped media structure that provides a long operating life as well as absolute filtration with a Micron Rating of .45. The structure of the Polypropylene bag consists of several layers of a medium that gets finer and finer from one layer to the next. With a SENTINEL Ring, this filter bag provides 100% bypassfree filtration and better performance for critical applications. Sold in box quantities of 4.