Flexible, galvanized, corrosion resistant, high strength steel alloy. Helically formed into a continuously interlocked flexible metal conduit that can withstand impact and crushing forces. Hot-dipped, heavy zinc coating for rust/corrosion resistance. Smooth interior for easy wire pulling. UL Listed, CSA Listed, NEC type designation - Article 348, Type FMC (flexible metal conduit), and meets federal specification WW-C-566c.