I know that there has to be a file about this. But Looking for it is making me dizzy. I have a poulan pro 4620 OEM 20 in bar and chain, I have been given 2 different file sizes. Both seam to fit like they would do the job, only one is just a tad smaller. The other saw is an older poulan Farm Hand 2900 2.8 ci with a windsor bar and chain, both of the files seam to fit with one being slightly smaller but looks like it would work. Having said all this, How do I tell what size file I need to do the job correctly?