Playing around this week a little. This isn't done yet, just a quick mock up to see what it might look like. Still needs to be surface ground to smooth the flats. It's about 4 inches long, CPM 3V, with a 15mm wrench for standard bicycle axle nut and room for one bit. I'm thinking 5mm for the insert bit but I may try another slightly different design and see if I can fit two bits in there.