Not much info on them it seems. They 'look' like the AZ STP XL filter. The former STP XL was made in S Korea by Daewha and were ISO rated 99%>20um. The newest/current STP XL which look the same on outside made in China and iirc the ISO efficiency rating no longer there. If it matters to you, website says 98% but no micron level, so doesn't mean much.