Described is a rotary coupling that includes a pair of coupling bodies having parallel (preferably coincident) rotation axes, two cylindrical elements and a preload mechanism. A gap is provided between surfaces on the first and second coupling bodies. The first cylindrical element is disposed on the first coupling body and has a first cylinder axis, and the second cylindrical element is disposed on the second coupling body adjacent to the first cylindrical element and has a second cylinder axis that is perpendicular to the first cylinder axis. The preload mechanism imparts a force to each of the first and second coupling bodies and thereby preloads the first and second cylindrical elements against each other at a point of contact. One example of the preload mechanism includes a pair of magnets disposed opposite each other across the gap and another example of the preload mechanism includes an air bearing.