Flare fittings can be used with copper tubing, iron pipe thread, and plastic pipe. Which material is NOT listed as compatible?

• A. Aluminum pipe
• B. Copper tubing
• C. Plastic pipe
• D. Iron pipe thread

Answer: (A)

Flare fittings rely on a properly formed flare on the tubing and a tight, metal-to-metal seal with a flare nut. Copper tubing is the standard material because it can be easily formed into a reliable flare and maintains a good seal. Iron pipe thread connections can be accommodated with adapters that bridge the thread to a flare seat, and plastic pipe can also be joined using appropriate adapters so the flare provides a secure seal. Aluminum pipe is not typically listed as compatible because it isn’t a standard material used with flare fittings in common water distribution practice; forming a reliable flare on aluminum can be more prone to deformation or cracking, and there aren’t widely used, approved flare fittings for aluminum in the same way as for copper and common plastics, making it an unsupported option in this context.