This is the Ultimate Racing pre-oiled dual-stage foam air filter, and it’s been specially designed for use with Xray XB9 air filter. The combination of this pre-oiled dual-stage foam air filter with the Ultimate Racing air filter oil guarantees the maximum air flow and offers an excellent air filtration and protection for your engine. Available in economic packs of 6 or 12 pieces pre-oiled and safely stored in a double zipper bag, so can be stored for long time and ready to use when you need them.