Coalescer filters have historically been specified by micron rating and percentage of retention. If you're not familiar with Filtration Grades for coalescing filters, here is an easy guide:

GRADE 4
Grade 4 coalescing filter elements are typically 0.01 micron with 99.99% efficiency. They are highly efficient coalescer filters used for elevated pressures or lighter weight gases. This is recommended when system pressure exceeds 500 PSIG.

GRADE 5
Grade 6 filter elements are used when complete removal of liquid aerosols and suspended fines is required. This filtration grade is most often used when system pressure is below 500 PSIG.

GRADE 7CVP
Grade 7CVP filter elements are made with two layers of filtration media. The inner layer traps dirt particles and acts as a pre-filter to protect and extend the life of the outer layer. The outer layer of media consists of a dense matrix of glass fibers which provide highly efficient aerosol removal. 

GRADE 8
Grade 8 filter elements provide high efficiency filtration in combination with high flow rate and long element life.

GRADE 10
Grade 10 filters are typically 1 micron. They are used as pre-filters for Grade 6 filters to remove large amounts of aerosols or tenacious aerosols which are difficult to drain. This grade is often used as a "coarse" coalescer. 

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