E-Z Lock® Insulated Snap-in Connector 3/8″, Die Cast Zinc
https://nsiindustries.com/product/e-z-lock-insulated-snap-in-connector-3-8-die-cast-zinc/
Use Bridgeport snap-in connectors to make fast, high-quality connections between AC/MC cable or flexible metal conduit and a box knockout. To install, just snap the connector into the knockout for a reliable connection – no tools required.