flex couplings
 

is it natural for the rag joints to become oblong or out of round? i can see them becoming maybe brittle or shredding from age. is the disfiguring from excessive torque from the engine? since there isn't any play going forward or aft, i would think that the holes themselves would become wallowed out and not the entire disk.:bigthink:

Mostly, well meaning folks overtighten the SELF locking nuts because they loose the self lock feature and that in itself distorts the rag joint.
Really they don't flex all that much.
They do absorb some shock load and allow for slight misalignment of drive angle. They use them because they are inexpensive and work well for many years.