new shift knob

i have a 54 belair powerglide i want to change the shif knob i kmow its not threaded on does anyone know the size of the end so i can order a new aftermarket one most that i have seen offer different size threaded knobs, i was thinking i can thread the lever but not sure what thread knob to get thanks vinny

 

i would say mic the shifter arm to see what size die to use. you will only have fine or coarse choice, most are fine thread i believe. then see that knobs are available. lots of aftermarket ones come with inserts to fit different threads. good luck.