M5x18.9 – M Shapes

M5x18.9 is 5 in (127 mm) deep with a 5 in (127 mm) wide flange, and weighs 18.9 lb/ft (28.1 kg/m).

M shapes are doubly-symmetric, I-shaped sections that fall outside the standard W and S weight/depth series — typically lighter and often smaller than the lightest available W shape at a comparable depth. They're specified for light-frame construction, secondary framing members, and miscellaneous structural applications where a full W-shape section would be heavier than the load actually requires. Because the M series fills gaps the W and S series don't cover, it's a useful option whenever a project needs an economical, lightweight I-shaped member — mezzanine framing, light equipment platforms, and similar low-load structural work.