Be sure to get a coalescing filter:
"Standard nominal five micron inline filters cannot remove
submicronic contaminants as required in critical
applications. The lowest particle removal limit for these
general purpose filters is 2 µm. Eighty percent of aerosol
contaminants are under 2 µm in size. Coalescing filters,
however, are specifically designed to remove submicronic
oil, water and solid contamination from compressed air.
Standard graded-porosity coalescing filters remove over
99.97% of all aerosols in the 0.3 to 0.6 µm range. In
addition, these filters are over 99.98% effective at
removing all aerosols and solid particles larger than 0.3 µm.
Thus, oil aerosols at a 20 ppm contamination level are
reduced to a 0.004 ppm concentration – acceptable for
virtually all pneumatic applications."
Great website on the topic: