i might just go ahead and buy some of the tr12x3, some bearings and couplers. does anyone know what internal diameter the bearings should be, ie. when i grind down the tr12x3 at what diameter does the thread disappear? i dont want to get bearings too big and end up with them supporting some of the thread. i assume the 12x3 relates to overall diameter and thread pitch so i dont know how deep the thread goes.