After filing, the ring will have a raised burr at the cut edge. This will cause the ring to hang-up in its groove, and can also damage the piston. A small, fine, needle file can be used to lightly de-burr the edge, but don't chamfer it. We used this de-burring tool from Childs & Albert, which works nicely. After filing, clean the ring and mark it with a felt pen with the number for its corresponding bore.