Yep not recommended for common rail motors, & unnecessary for cars that get their fuel in populated areas, but filtration is a bit better than 12 microns I think, at least according to this according to this.
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Mind you I have read claims they are as low as 2 microns elsewhere on the 'net (have my doubts about that though - I would think that may well affect fuel flow). My guess is that along with the variety of brands of filter that fit these CAV type housings there is probably a variation in micron ratings. Bottom line for me is that it works as per my previous photo & with no fuel flow issues using the stock GU fuel pump & no additional lift pump. That photo was after around 10,000kms. As a result I decided to change the CAV every 10,000 & the standard filter at 20,000, I'm yet to do that though. If I have the means to cut open the standard filter when I next change it I will, & if it looks clean enough may up the next change interval of the standard to 30,000kms.