Racor Replacement Element for Diesel Gas Spin-On Fuel/Water Separators 

The lower the micron rating, the finer the filtration. Follow your engine manufacturer's recommendation for fuel filter micron rating.
S = Secondary/Final 2 micron (Brown cap)
T = Primary or Secondary/Final 10 micron (Blue cap)
P = Primary 30 micron (Red cap)

Color: Brown, Micron: 2, Fits: 120A, Case: 12