The In-line filters that I supply have a finer “mesh” than the brass ones and are replaceable – think of the “Gunk” that has built up in a 55 year old fuel tank and rubber pipe system.
My advice is to change every time they look full of detritus.
See: http://traction-owners.co.uk/images/classifieds/CIMG1231.jpg
More information at the bottom this page:
http://traction-owners.co.uk/ads.shtml