Likewise - it's a standard stud threaded into a nutsert, and should be threaded 3/8"-16 (earlier models) and either M8-1.25 or M10-1.0 (later models, not sure when it would have changed from SAE to ISO.)
Using the "double nut trick" allows you to remove the stud in a condition that may be reused - using a "stud puller" generally wrecks the threads.
"Double Nut Stud Removal":
Select two full-height nuts that fit the stud threads.
Install one nut about halfway down the length of the thread. You won't want to get right down to the installed surface, as you'll need room to get a wrench on the lower nut.
Install the second nut against the first. Using two wrenches, tighten the nuts against each other firmly (you're going to need heavy resistance between the nuts in order to back the stud out.) Optional: You may install a flat washer between the nuts for convenience. This will ensure that you can grip only one hex nut at a time with your wrench.)
When you have torqued the nuts together, place your wrench on the lower nut (farthest from the free end of the stud, closest to the surface the stud is protruding from) and turn it anticlockwise (unscrew direction.) If the nuts turn but the stud does not, tighten the nuts against each other some more. Repeat.
TIP: If you've got the two nuts cranked against each other as hard as you feel you can, remove them. Get out a propane or a MAPP torch and a block of paraffin wax (NB: Also have a replacement stud. This is going to wreck the stud you're removing!) Heat the end of the stud - do not heat the part it is installed into! - until it's at least a dull red. Remove the heat, and touch the paraffin block to the juncture between the stud and the installed surface. The paraffin wax will melt and run into the space between the stud and the internal threads - also, heating the stud will force expansion of the threads. Let the stud cool, reinstall the nuts (and washer between, if you wish,) and re-attempt removal. Should come right out this time. DO NOT reuse this stud! Throw the old one in the scrap bin, and install a new stud. By heating it red hot, you have wrecked the heat-treatment of the thing, and you may as well install a heavy-duty plastic instead. If I have to do this, I don't trust it for anything structural anymore...
When installing the new stud, coat the threads with something - if there's no torque spec given, using never-seez should pose no trouble. You may also use RTV, plumber's PTFE paste, or even chassis grease (although this is a "last resort" option.) This will help you get the wretched thing out next time - you can safely assume there will be a next time...
If there is a torque spec given specifically for installing the stud, use LocTite or RTV (no modification to torque spec, but will help prevent future seizure) and you may repeat the double-nut trick to install the stud. Turn the outer nut to install the stud, and be sure to hold the inner nut when you go to break torque between the nuts to remove.
