When sourcing MJ pipe fittings, the most critical factor is the material grade, typically Ductile Iron (ASTM A536), which provides superior tensile strength and impact resistance compared to standard cast iron. You must verify the pressure rating (e.g., Class 150, 250, or 350) to ensure it matches your piping system's requirements. Additionally, check the coating type; high-quality fittings usually feature fusion-bonded epoxy (FBE) or bituminous coating to prevent corrosion in underground or high-moisture environments.