A "heads up" for anyone buying the PT&G drill with the (female) threaded end. Very nicely made tool by the way but it comes with no instructions and for a first time user there's something waiting to bite you in the ass:
Female threads are fairly deep (.500 maybe) in a counterbored (shouldered) hole. Make sure your threaded portion is long enough to bottom out in the hole before the shoulder of your rod bottoms in the counterbore. I made that mistake, - shoulder of the extension rod bottomed before threads bottomed. Cutting forces wound the threads deeper, shoulder of the extension rod expanded the counterbore, splitting off the side of the threaded hole. Not a happy day 
I saved it by silver soldering everything back together and "making it work" but not pretty.
By the way, I had to re-sharpen the drill a couple of times during the process (which surprised me) - it was a 1915 Stevens Favorite .25 rimfire I was putting a .22 liner into. Must have had some hard spots in it.
Can't really blame PT&G for it, I just never anticipated that the extension rod would screw itself deeper into the hole and bust out a side of the counterbore. Lesson learned !