Well, you can use the tap to do the bulk of the work but you will have to finish it with a boring tool to do the relief groove and an internal threading tool to finish about the last three or four threads. And picking up the lead will be ticklish as you will have to loosen the chuck jaws, engage the half nuts, take out the backlash, and rotate the part until with jaws tight, the ID threading tool exactly fits the thread. Cut the relief groove before doing this. Otherwise, the protector will not screw onto the spindle far enough.
Or alternatively (and what I would probably do in similar circumstances) is to make the relief groove wider than it would normally be so that when turned into the protector as far as it will go, the first full thread on the tap has cut just through into the groove area.
