Liquid Tight Sealing Ring 4″, Polyethylene, Steel Retainer
https://nsiindustries.com/product/liquid-tight-sealing-ring-4-polyethylene-steel-retainer/
Use Bridgeport sealing rings to make liquid tight connections between liquid tight connectors, raintight connectors or threaded conduit and a box knockout. The polyethylene gasket and steel retaining ring keeps water out when secured with a locknut.