Lintels of ½- by 3-inch flat iron bars. 3½- by 3¼- by ¼-inch
angle irons, or damper frames are used to support the masonry over the
opening of ordinary fireplaces. Heavier lintel irons are required for
wider openings.
Where a masonry arch (fig. 38) is used over the opening, the jambs
should be heavy enough to resist the thrust of the arch. Arches over
openings less than 4 feet wide seldom sag, but sagging is not uncommon
in wider fireplaces, especially where massive masonry is used.