A diaphragm coupling having first and second diaphragm plates that are joined together around their outer edges. Each diaphragm plate has a central, axially-extending hub. The hub of the first plate supports within it a pin member having an outwardly projecting shoulder at each end adapted to engage an internal shoulder on the hub of the first plate at one end and an internal shoulder on the hub of the second plate at the other end so as to limit axial separation of the two hubs—from one another.