I have these hook sharpening files made to my specifications so they will sharpen all flies from size 24 up to 2/0. This is the best hook sharpening file made and the only one I use.
I use my Murray's Hook Sharpening File to sharpen the hook of a new fly when I first put it on my leader. Then about every half hour I check my fly and sharpen it again if needed. This is very important at this time of the year when we are fishing nymphs and streamers deeply because they often strike rocks on the stream bottom. I use this same file to sharpen midges from as small as size 24 up to streamers as large as 2/0. I am often asked, "How do you attach this file to your vest?" Good question. There are several ways you can carry it. 1) Put it in the pocket of your vest (pointy side up so it doesn't create a hole in the bottom of the pocket or 2) tie an old piece of string or fly line around the sharpening file and hook to your retractor/zinger on your vest or chest pack (my preferred choice).