That's a 30 amp replacement Male plug for a trailer's shore power cord.
I installed one on our cord...they are easy to connect, be sure to observe correct polarity for the hot, neutral and ground leads.
I did run into one problem...the Gripper has a 'u' shaped prong for the Ground...and most RV Female connections are made to accept a 'round' prong.
I couldn't connect the new Gripper to an RV extension cord because of this different Ground prong configurion...I used some heavy pliers to try and modify the 'u' shaped prong into a more 'rounded' cross section shape...it works, but the Gripper is really 'tight' when plugged into an RV extension cord, and is hard to remove without a pry bar or screw driver to pry the plugs apart!
The Gripper is a good idea, but they could have made the Ground prong round like all the other plugs...IMHO!
Ray & Pat; Morada, CA