Directions given by Nick Cook and others say to start with an 1 5/8 hole, then a 1 1/16th inch hole and finish with a 1 inch hole all the way through the blank. They also then again bore a 1 1/16 inch hole in the top to allow a larger tenon into the body of the mill.
Why not just go all the way through with the 1 1/16th? Is it to be able to have a thinner mill where people grip it? Doesn't seem like 1/16th of an inch makes much difference and it sure seems easier.
Dave Fritz