This product is advertised as 4 pockets but has 3.  This makes no difference, however it's why 4 rather than 5 stars.  The item is marked 1 micron filter on each pocket though I saw no JDS marking.  The Delta filter it replaced had no Delta marking either so this may be typical.  The filter fits my Delta 50-860 perfectly.  It should fit the 50-859 also since they are the same size.  This filter appears to be better than the Delta filters but I have no way to measure this.  I'd buy this again from the same seller.