Specifications Hankison Coalescing HF Series: Grade 3 Ultra High Efficiency Oil Removal Filter For coalescing ultra-fine oil aerosols; removes solid particles to 0.01 micron (0.0008 ppm w/w maximum remaining oil content). Corrosion resistant inner and outer cores. Coalescing (Pre-Filter) Filters Often called the pre-filter since it is placed on the air line just prior to the air dryer, a coalescing filter removes oil, particles and moisture before it can come in contact with the desiccant in the dryer and ruin it. Our Coalescing Filter Replacements come with a manufacture's warranty that matches or exceeds the original OEM warranty. Original equipment manufacturer (OEM) names are the trademarks of each manufacturer. On products marked "replacement," OEM names and part numbers are for reference only.