US Patent 9359831 Top drive main shaft with threaded load nut

A top drive system is provided. In one embodiment, a top drive includes a drive stem and a load nut with mating threaded surfaces that enable the drive stem to be threaded through the load nut and to support weight of a connected drill string via the load nut. One or both of the mating threaded surfaces may have a threadform with one or more undercut thread roots. Additionally, a portion of the mating threaded surfaces, such as thread roots of the drive stem, can be shot-peened. Additional systems, devices, and methods are also disclosed.