Enzo101,
As TehNguyen said the shift knob thread for the GT350 is 10x1.25. If you are asking because you want to change out the OEM knob I have been down that road. I wanted a White Ford Racing Round Ball. I was only able to find them with the 12x1.25 thread so I got a 10x1.25 time-sert which I screwed on over my GT350 shifter. Now I can use any 12x1.25 threaded knob out there.