1-Gang Fire Classified Steel Floor Box. Adjustment range over deck of 2'' (51mm) minimum to 5'' (127mm) maximum. Use in normal weight concrete 4 1/2'' (114mm) minimum pour over deck. One 1 1/4'' (32mm) conduit feed opening. Box Capacity 53 cubic inches. This floor box preserves the 2-hour fire rating of floors in which it has been installed.