flared fittings

Hi all,

I'm back with another question. Can you tell me the difference between the thread on a flared fitting and a regular ips thread. Also what the difference is in the sizing...e.g. 1/2".

Thanks to all youguys for helping us dummies out.

The thread on a flare fitting is a 'running' thread, like a bolt. Running threads are also found on compression fittings, slip-joints and the converge of unions.

Iron pipe threads are tapered, meaning they are smaller at the tip of the thread. The corresponding fittings are inversely tapered, meaning they are larger nearest the opening. These fittings seal by interference, meaning the male threads on the pipe mesh with the female threads of the fitting.

Running threads have no sealing properties. They are merely there to help 'sandwitch' the pipe to a ground joint connection.

Running threads and tapered/ips threads are incompatible with each other.

There is not correlation between the various types of threads found in plumbing fittings: IPS, NP straight, compression, flare, union joint, etc. Size callouts can also be confusing. For flare and compression, the size reference is to the OD of the tubing used. Obviously the diam of the threads themselves is larger. Pipe threads, the size reference is to the nominal ID size of the pipe.