Thomas & Betts 4052-BRN Round Flat Blank Box Cover Thomas & Betts 4052-BRN Round Flat Blank Box Cover Features: Plaster cover with flat back for 4" round boxes and outlet boxes 3-1/4" to 4" diameter round flat blank with 4" outside diameter 150º C heat rated material Classified for two-hour firewall and fire-ceiling Brown 3-1/4" round