Threaded Fixation Nut 3/8" (with collar) to fit Synchron Motors This threaded fixation nut fits a threaded shaft 9.5 mm (3/8"). Largest diameter is knurled on the outside, outside diameter is 15.9 mm (5/8”). The collar is smooth with a diameter of 11.9 mm (15/32"), total height 5.2 mm (13/64").