[SML] What is this cap called?

[billn at peak.org]

> Anyone know the official name of one of these screw-on caps? It goes on the
> end of the pickle plug on my Electrics winch control.....
>
> I need to replace it, but I'm just wandering around the McMaster-Carr site,
> trying to figure out what it would be called....

It probably goes by something like receptacle cap or plug cap.

Why do you need to replace the one you have?

Bill