None of those dimensions are that critical. The 3/4" shaft needs to be long enough to be held securely by the collet, but not so long that it bottoms out. The flange needs to be deep enough to sit on the square portion of the spindle instead of against the collet head, but that's it. Any variation between your tool holders will be compensated for by your tool height table.
Set screws on tool holders are usually around 1/4" or 6mm in diameter, but you'd use smaller ones on toolholders for small endmills.