A locking assembly for fastening two components together, such as a fluid coupling assembly, is disclosed. A first member has a serrated annular surface and fastening threads adjacent a bearing surface. A second member has a flexible projection or projections or a complementary configuration to the serrated annular surface. The second member also includes fastening threads and a bearing surface. When the respective threads engage, they provide the primary preloading force to the bearing surface, while simultaneously the projections and the serrated detects provide a retention force to ensure a positive coupling.