The Sundstrom SR 221 pre-filter is a non-classified filter media designed to capture coarse and larger particles while extending the life of the particulate filter SR 510 and SR 710. The pre-filter is placed in the prefilter holder which attaches to the particulate filter.  Sold in pac of 5 or box of 80.

Click here for info sheet: https://cdn.shopify.com/s/files/1/0055/9454/6294/files/SR_221_PreFilter_info_sheet.pdf?v=1710189604