These items appear to be N-Eupex coupling elements (or a similar jaw-type flexible coupling) designed for transmitting torque between machine shafts.
They consist of a rubber or elastomer component with "H" shaped projections that fit into metal hub flanges.
The components help dampen vibration and absorb shock loads between connected industrial equipment.
They are available in various sizes, with some sets consisting of 6 individual pieces made of nitrile rubber. [1, 2, 3, 4]