This cutter is designed to make keys for locks after you decode them with a Lishi pick, but it can also be used to nibble cuts into standard brass keys while impressioning or originating a key by hand. The cutter has markings etched into the cutter head to gauge the depth of cut. This tool makes a clean V-shaped cut with a flat bottom so your pins or wafers seat nicely. Faster than filing, this tool has a series of lines on the head to help gauge your cutting depths. Compact design is  7-1/8” long x 2” wide.  Here is a video of a guy using them. 

https://www.youtube.com/watch?v=6RAU00AKLCQ