Picked up a cool little file set today at Harbor Frieght. Under ten bucks and includes 10 needle files, 2 of which are jewelers size rat tail files that work great for filing/cutting a round bottom slot in a bass nut.
The 2 diamond coated rat tails measure .144 and .122 at the thickest point but taper down to a useable .053 at the tip. The skew number is 06989. Just touched up a couple of nuts, one brass and one bone, and they cut like butter.
Glenn in Texas