When evaluating a factory, prioritize Hot-Dip Galvanization (HDG) over electro-galvanizing, as HDG provides a thicker zinc coating (typically 60-80 microns) essential for rust prevention in outdoor environments. Ensure the base material is Q235 or Q345 carbon steel for structural integrity. For the finish, specify AkzoNobel or Tiger brand powder coating to ensure UV resistance and prevent peeling. The railing height must strictly adhere to local building codes, usually minimum 1100mm for residential balconies, with vertical picket spacing not exceeding 100mm to ensure child safety.