L1430C
Hubbell Wiring L1430C NEMA L14-30C Conn 30A 125/250V
It's exactly 1/4 in, which means no shimming or adjustments needed.
Hubbell Bryant Twist Turn Lock Connector Plug NEMA L14-30C 30A 125/250V L1430C
This plastic item is dishwasher safe, so cleanup is as easy as tossing it in the rack.