Insulated Bushing, 3-1/2″, Malleable Iron for Box Termination
https://dev.nsiindustries.com/product/insulated-bushing-3-1-2-malleable-iron-for-box-termination/
The Bridgeport 3-1/2″ Malleable Iron Insulated Bushing can terminate threaded rigid or IMC to a box using a simple locknut. It features a plastic metaliner that prevents damage to wire insulation.