After busting my knuckles trying to loosen the locking bolt of the alternator tension, I tried using a 12mm socket on a 1/4" drive ratchet. I could only do this with the help of my wife being my paws were too big. The 12mm bolt that creates the tension for the alternator was easy enough, 12,, socket, a 3/8 universal joint drive two of my longest 3/8"drive extension bars and the 3/8" drive ratchet. I used the 90 degrees turning of the alternator belt as an approximate tension adjustment. No more squeal !
I have the Lexus 1999 RX 300. Used a Gates belt, sold at NAPA
HAPPY MOTORING

 

Good to hear and Welcome to the Club.