A lock nut assembly 10, 10′ has a first component 12 provided with a threaded axial through hole 19; and a second component 14 provided with an axial hole 31. The first and second components 12, 14 are detachably coupled together and arranged so that both components are simultaneously engagable with a common tool to effect application of the assembly 10, 10′ onto a threaded member 22 by operation of the tool to impart torque to the assembly 10, 10′ in a first direction. The first component 12 initially engages the threaded member 22 with the second component 14 following. The first component 12 provides fastening to the threaded member 22 and is torqued as required. The second component 14 acts to lock the first component 12 onto the threaded member 22.