As far as I have been able to find out the secondaries on my SP225s are between 5 to 7 micron and you can’t buy a specific micron like with a Racor. The manufacturers of the secondary filters don’t specify a micron rating as far as I could ever find. I use a 10 micron primary element in my Racors and then I don’t have to change the secondaries as often. My Racors are simple to change filters, the secondaries not so much.
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