A new approach, the dual-centric rotary stem joint from Fluid Dynamics System, Winston, Ga., uses a stem adapter that has centered and off-centered bore sections. The shaft to be attached gets machined so that it ends in a smaller, off-center shaft on a centered shaft. Fitting the two together lets the joint transmit torque or rotary motion. There is no minimum or maximum size limit. The joint survives high vibrations, periodic loading, and quick reverses in rotary motion. It takes no special equipment to assemble or take apart. The adapter can be double ended, with centric and eccentric bores on each end to connect two shafts machined to accept the adapter.