NEMA L14-30P Twist-Lock to 14-50R RV/EV Adapter
New compact design! This fully molded adapter features a NEMA L14-30 twist-lock plug on one end, and with a NEMA 14-50 (50 amp) receptacle on the other. (Note, photo shows two adapters so you can see both ends, but they're sold in single units.)
The L14-30 twist-lock receptacles are a common generator outlet, and are sometimes used on racks of power amplifiers in large audio systems.