E-Z Lock® Insulated AC/MC Connector for Old Work 3/8″, Zinc
https://hotfix.nsiindustries.com/product/e-z-lock-insulated-ac-mc-connector-for-old-work-3-8-zinc/
Use Bridgeport double-snap snap-in connectors for old work to make fast, high-quality connections when installing AC, MC or FMC into an electrical box or enclosure. Snap-in design requires no tools for a complete installation.