General Tools & Instruments 4 7/8 to 4 Circle Cutter
Combination round and square shank circle cutter that acts like an adjustable hole saw for use with drill press or bit brace.  This tool has replaceable 3/16" high speed steel bit and replaceable 11/64" pilot drill with maximum safe speed of 500 RPM.  Sizes:  7/8" to 4"; 3/8" round shank.