A fastener assembly for use in locking relationship with an internally threaded member is disclosed which includes an expandable bolt having a cavity extending longitudinally therethrough which is cylindrically shaped on a first end segment thereof and frusto-conically shaped on a second adjoining end segment thereof. The assembly also includes an elongated draw rod having a cylindrically shaped end portion adapted for close fitting slidable engagement in the first end segment, and a frusto-conically shaped end portion or boss having a rate of taper which is greater than the rate of taper of the second cavity segment. The bolthead defines a first circularly shaped recess concentrically formed about an opening of the cavity and a larger diameter second circularly shaped recess essentrically formed around the first recess. A nut which engages a threaded end portion of the first segment of the draw rod is retained in the first recess and a split locking ring which is disposed about the nut is retained in the second recess such that the ring ends become jammed between the nut and a peripheral defining wall of the second recess as the ends of the locking ring are rotated into a narrow portion of the second recess as the nut is tightened on the spindle.
