According to thenooblord, the piece is totally irrelavant and you should not put any further thought into it.
In all seriousness, its a ratchet to keep the gears spinning in one direction only. To install it you hook one end of the spring on the back side of the latch, and compress it against the side of the wall with the latch as you install the bevel gear. To ensure you have installed it correctly, remove the piston and spring and attempt to spin the gears (while holding the anti reverse latch down with a finger) and see if it "ratchets" with the gears.
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