I place a thin 14mm (IIRC) wrench on studs shaft nut (red arrow point to), to hold stud. Then six point socket or box end wrench, on securing (fastener) nut.
If you've alternator out with securing nut, stuck on the stud). You can remove the nut from stud in most cases and reuse the stud.
I place a "thin" open end wrench, on studs' shaft nut (red arrow picture above). "Thin", so it fits between stud shaft nut and alternator. I've ground thin, a open end wrench, just for this alternator stud.
With alternator out. One can, clamp on stud along shafts in non threads area if one doesn't have a thin open wrench or wrench is not holding well enough. Or use both the thin open end wrench and clamp on studs shafts. This yields a supper hold on stud.
Then clamp on the damaged 12mm securing nut with either a: Six point box wrench, six point socket, nut extractor socket, vise grips or vise. Unthread nut off the stud.
I install the stud with a little red thread-locker on its threads (side that threads into block) and torque to 11ft-lbf. with long socket.
Thread sealer is a lube. We see red sealer on threads in picture of new stud. So I don't reduce torque 20% to 30%, for lubed threads.
Alternator Toque: 12mm fasteners 12ft-lbf.,14mm 29ft-lbf. Note: 98-02 have two fasteners (securing nuts & bolts) points, 03-07 have 3 fasteners points.
Vane pump (steering pump) 14mm bolts (3), torque 13ft-lbf. (Note 2005 FSM. Has this wrong in one spot, at 54ft-lbf.)
One thing not shown in video and so often missed by DIY and shops. The wire hanger bracket, must be swapped over from old alternator.
I've never bought one of these studs. But this should be it.
Make sure to match with your bolt/stud. If near a dealership, just order from them. Tell them which bolt, they should get correct P/N.
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Toyota 90109-08298
Bolt
Alternator wire hander bracket. Must be swamped over to new alt..
Main hot wire is keyed. Place keys of wire end in slots of alternator. Torque nut to 7ft-lbf. Best the protective cover clip on cover stub/wire end/nut. Exposed is a fire risk. Snap in wire harness, to hanger bracket. This keeps wire from bouncing around.