Insulated Throat Box Connector | 4 in Square Plenum Box Cover; Blank With Gasket and Two Captive Screws | Steel Box Connector for 1/2 in Knockout, 3/4 in Single Ac, Mc or Flexible Metal Conduit, No Locknut Required, Captive Clamp, Integral Red Plastic Insulated Throat Bushing,Furbay Electric Supp