The extensions on mine came from thor, and they are a pain in the neck
Just like Dave mentioned above, they are positioned so as to be really picky about getting the chuck engaged. Only a very few will even work.
Also, I had a problem with leaks, so eventually I removed the extensions from the inner wheel.... done with the help of my 9 year old's small hands.... in a cracker barrel parking lot
Now I can get a straight chuck on easily, but I can't get a dust cap on since the holes in the simulators are a bit too small. A lot of the problems are because of the wheel simulators btw....
My outers still have the hooked extensions in place, although one has a habit of swing around 180 degrees from the desired position so that I have to reach in the small hole and swing it back to get at it.
Honestly, i have been a bit indecisive as to what i want to do.... my thoughts are;
1) enlarge the holes in the wheel simulators so that a hand can get in there (this will almost certainly bugger up the chrome and not look good)
2) install a Crossfire unit ( which are not designed to mount to simulators, so a modification ...ie hole... will be required). I'm concerned that this will add another potential leak just as the now removed extensions did.... although many folks use them succesfully
Crossfire - Dual Dynamics
&/or 3) install a TPMS
Honestly, what i'd like to do is to do both 1 & 2, and follow up with 3 later (only to minimize the money going out all at once)