This is the Ultimate Racing pre-oiled foam air filter, and it's been specially designed for use with Mugen MBX8R air filter. The combination of this pre-oiled 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.