The Atop square filing jig shows you the angels you need to square file chainsaw chain.I bought one not to long ago it works pretty good. The Atop kit comes with jig and 2 four sided files and one round file. The cost is about 220 bucks with out shipping I got mine from baileys. If you google search Atop square file jig you tube will give you a couple of videos that will realy help useing this jig.