If you mean the belt tension pulley, on my 2000 GT-s it is a 19mm socket or boxed end wrench. I shaved down a socket to get it to fit good. But also on that, my belt has done the same thing for years. I have changed many tension pulleys and belts, it still happens. What I have started doing is spray belt conditioner on the belt every time this happens. It goes away for a few months. Mine mainly happens when I have the A/C on.