As a more serious aside, I would suggest that rather than ONLY operating the Half-nuts to stop a threading operation, get used to using both the half nuts and the cross slide simultaneously.
I generally set my cross slide with the crank handle at either the top, centered, or the bottom, centered, so it is very natural to crank one full turn away from the work, at the same time as the half-nuts are disengaged. You should only be using the cross slide screw for setting the tool at it's "Zero" point, and returning it to that point for the next cut, with all the actual infeed being taken care of, using the compound. Disengage everything, slide the carriage back to it's starting point, spin the cross slide TWO turns across it's "Zero" then once back in against any backlash so you can set the cross slide ON the Zero, feed in the compound, for the next cut, wait for your index mark to roll around (if the thread is not evenly divisible by the pitch of the lead screw, on inch machines!), and engage the half-nuts when you so desire.
You can use the same rhythm of the chuck, to set the speed that you crank over the handle on the cross slide, and you will very soon find that you stop worrying about things like blind holes and shoulders.
Stuff happens! Fiddling with both the cross and compound feeds, is a skill worth developing too, as you use that for picking up a thread that is already on the part, if doing a repair, or picking up your thread to continue it, should you duff the tip off of your threading tool, and you find yourself doing a regrind. ALL of the apprentices I taught, were thoroughly un-excited about breaking a tool, or having to otherwise pick up and existing thread, once they had a couple goes at it, and it was no longer a 'scary' thing! Especially in Repairs, being able to pick up a thread is a really handy skill, and a bit of practice at it (like thread cutting itself), goes a long ways to taking the fear factor and, well, pretty much destroying that!
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