Dual filter base

[LowTech]

Been looking at dual filter bases for our WMO filtering. The question that I have is how do I tell if they are in series, or parallel, or are they all in series?
I'm finding links to units w/ very little info.
And what would be a good size for the spin on filter mount point, one that would let me use the most common filters.

Thanks all,

 

[Wildchild467]

i filter in series. 25 micron, 10 micron, then 5 micron. surpluscenter.com has some nice filters/bae combos. i bought some of the big filters that flow something like 40 or 70 gpm and screw into 1.25" pipe. they work well for me and filters are not that expensive. i took the specs of the filters (dimensions) and cross referenced it to a napa filter and thats where i bought my 5 micron filter. i've filtered a lot of oil and have not had to replace a filter yet.