4" Diameter, Nail-On, Ceiling/Fixture Box with "N" Bracket, Phenolic, Depth: 1-5/8". Cubic Inches: 13.5". Includes: Nails, Clamps. New Fire Rating. Carlon phenolic boxes can be installed in the same stud cavity of a shared two-hour wall. They may also face opposite directions with only a 3" horizontal separation.