Sundström SR221 pre-filter Holder (PACK OF 5)Pre filter in front of the main particle and gas filters. The low cost pre filter sorts out coarse wet and dry particles, protects the main filter and prolongs its service life. Material: Polyester. Size: 102 mm diameter; 1 mm thick. Fits into the pre filter holder of all Sundstrm non threaded main filters (gas and particle). Storage: Store at room temperature in clean, dry place. If seal has been broken, store away from contaminants in an air tight