Methods and systems for retaining bonnets on blowout preventers. In one embodiment, a blowout preventer includes a hollow body, a ram disposed in a ram cavity of the hollow body, and a bonnet coupled to the hollow body. The bonnet is fastened to the hollow body with threaded fasteners, which include a threaded shaft and a threaded nut. The shaft and the nut include mating interrupted threads with threaded portions and longitudinal unthreaded portions that can be rotationally aligned so that threaded portions of each of the shaft and the nut are aligned with unthreaded portions of the other of the shaft and the nut to allow the threaded shaft to be received within the threaded nut and the threaded nut to then be rotated with respect to the threaded shaft to cause the threaded portions of the threaded nut to engage the threaded portions of the threaded shaft.