I’m at a loss

[Mad Professor]

I bought a TC with a Mag Spark type primer adapter and found it was removable by a hex (Allen) wrench inserted down through the nipple.

This is correct. There's a hex shape in there and the appropriate sized tool should take it right out.

I have removed several of these by unscrewing them with an Allen wrench as was stated above.

Glad someone has current experience and/or remembered how they install

I bought one of those many moons ago. When I found out what a PITA it was I never ended up using it. It's sitting in the back of drawer someplace with other ML parts. I couldn't remember how it got tightened.

I didn't chuck it, as if for some reason the sources of #11 caps dry up, at least I'll still have 209s as an option.

I always carry a candle with me when hunting, and wax around the nipple/cap to keep out moisture.