[Animats]

That's the latch, not a key. Keying prevents putting the wrong plug in a receptacle. Usually that's done with notches on the receptacle and ridges on the plug.

[themaninthedark]

You can use the ridge that the latch attaches to as part of the key structure.

There is also a J-shaped structure inside the plug that would function as a key as well, prevents the plug from starting when rotated 180 degrees.

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