Flat Cover | 4 in Octagon Back Plate With No Stud; (3) 1/2 in Knockouts, (2) 3/4 in Knockouts | For Use in Insulated Ceilings | Use Through Knockout to Connect Box to Conduit Coupling; Use With a Locknut to Connect Two Boxes Side by Side or Back to Back; Use With a Locknut to Connect Fixture Housings in Continuous Runs; Rigid Conduit Threads (Nps)Furbay Electric Supp