It's a twist lock style plug. The bare plugs can be found at most electrical supply stores if you want to use it, or make an adapter.
I sort of wish that they had used a regular electrical plug that was just able to supply more than 15 A instead of using that funny plug though, as there's lots of times that I've needed more amps than what one generator will supply (air Compressor for example) but I'm not actually able to plug the draw into the parallel kit due to the lack of a standard receptacle.
One of these days I'm just going to go buy a twist lock adapter, a small length of heavy cord, and a regular 15 amp female plug and make an adapter.
Then again on second thought one of the RV 30>15 amp adapter plugs would probably be cheaper.
