FINE CUT ROUND FILE, EXCELLENT FOR KEY IMPRESSIONING
A fine cut round, or rat-tail, file is very important in the locksmith shop, especially if impressioning keys is part of the job. Most locksmiths will have a set of files on the work bench and another set in each service vehicle.
A fine cut round file like this one (number 4 cut) is essential if you originate keys via impressioning. The round file is typically used to get a cut started. Once the proper depth has been determined (impression marks get very heavy) a Pippin file is the best choice to shape the cut.