l think in the above post that grm61 links I gave the inner pn# I now have close to 600 hours on the tractor with no issues. The Bobcat brand comes from the factory with the inner element, that is where I found the part number. Like I stated in the link I have never worked on a piece of heavy equipment that did not have a inner and outer element. When I purchased my D3 cat dozer it had the outer element partially failed, if it did not have a inner I am sure the engine would not have been in good shape considering the dirt packed in the inner element. Cheap insurance. CJ