Ian, I work in the filtration industry and to put in perspective, modern oil filters are rated 15-20 microns (the smaller the number the more efficient the filter) Typically, a human 'grey' hair is approx 50 micron looking end on, strangely grey hair is thicker than dark hair. 600 micron is a sieve and will stop bearing fragments etc but little else, certainly never restricting flow unless your using treacle for oil. Hope this reassures you. Pete