I run the clunk/filter that Jim linked to here as well as this inline filter -
http://www.horizonhobby.com/Products...?ProdID=HAN143 which is compatible with both gas and glow fuels. While I can't tell you what micron size the screen element is, it appears much finer than the metal screen versions. Since going to this setup, I haven't found anything inside the internal walbro carb screen.