This flap stay is superbly engineered.
Essentially a uni-directional viscous coupling, it turns freely in one direction, and hydraulically slows movement in the other direction.
Inside the sealed body are eight slotted steel discs that control resistance. A thick, sticky fluid is forced through successive discs, creating resistance much like a shock absorber.
A much better design than typical sprung stays.
9" long overall.
Supplied with mounting hardware, screws, and instructions.