They are Lovejoy couplers. McMaster-Carr.
You have to select each half separately, based on each shaft's size. Then you get a spider to join each half. It is just a buna or urethane star-looking thing.
IIRC, I got everything for under $15; with one of each type of spider material.
I can send you the part numbers/pages when I get home tonight. Headed out to SWMBO's Vegas-Night type Christmas Party. If I can't get back here tonight to post it, it may have to wait for tomorrow.
