Snap-In Connector, 1/2″, PVC for Portable Cord to Box
https://dev.nsiindustries.com/product/snap-in-connector-1-2-pvc-for-portable-cord-to-box/
The Bridgeport 620-NM 1/2″ PVC Snap-In Connector connects a nonmetallic portable cord to one 14/2 to 10/3 cable or two 14/2 to 12/2 cables to box applications without a locknut. Made in the USA, the connector is 1-3/8 inches long.