Five Micron Pre-Filter used in most of our watermakers that we manufacture. Check dimensions to make sure it is the correct Filter: 2.5" x 9.75". These filters are used for seawater applications, no other type of filter should be used as it may cause permanent damage to the RO membrane. These are a non-cellulose pleated filter with a rigid core built for harsh seawater conditions. You will need to change your pre-filters when they start to clog, how often you change the filters depends on how clear the water is that the filter is used in.