As you can see the jack has a smaller diameter thread sticking outside the guitar body, and a little shoulder that needs to land just below the exterior surface:
Once he gets the depth set, Mike returns to the outside to solder up the wiring.
One drop of hot solder would burn clear through even the strongest finish, so all the hot work gets done with plenty of protection for the guitar!
Two layers of bath towel may be overkill, but it never hurts to be safe!
Mike's soldering the connections from the pickup sensing unit wire, which is just long enough to allow working outside the guitar once the sensing unit is installed:
After soldering up, he can tighten the jack in place:
There's a little nickel plated cap that screws over the jack to become the strap holding end pin:
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