Used the Eagle R&D supplied fuel filter as an oil pre-filter to protect the oil pump from any possible contamination arising from the oil tank. Other builders have noted instances where foreign objects have blocked the flow of oil to the engine. The main oil filter is placed after the oil pump and strains the oil prior to returning it to the sump. This filter is inline prior to the oil pump. I ran oil flow tests to check on how restrictive the filter would be with Progear 90 wt. oil. At 40 deg. F. the filter restricted the flow by 20% which is probably not significant at normal engine temp. and viscosity.