50mm or 2 inch cutting profile should be plenty bro with a 40mm long 1/2 shank. The overall diameter of the cutter depends entirely on what size bearing you use on the bottom whether its a 1/4, 3/8ths or 1/2, the bigger the bearing the bigger the diameter of the cutter as you have to follow the curve of the diameter and the cutting length ie 2 inches, so the diameter will depend on where the cutting profile ends if you see what I mean. I would probably not go for the 1/4 inch bearing but more for the 1/2 so the overall diameter of the cutter will be about 19mm if I'm correct. Maybe just maybe the firm that you are using have 19mm diameter cutters already that can be adapted by fitting a 1/2 bearing on the bottom and then working the profile or grinding it this ? Also please remember the cutter profile must be "EXACTLY" perpendicular to the fretboard that you will be radiusing as if this is off you will end up with the cutter cutting a more sharper radius than you intend. Bro PM me and give me you e-mail addy and then I can send you a sketch of what I mean, a picture is worth a thousand words, again many thanks and hope this venture makes you a nice little earner as I'm sure everybody will have some at a good price. I would love a full set from 7 1/4 inch radius to 16 inch radius as I use a variety of radiuses on every build that I do, many thanks again.