Douglas, this fitting is marked and intended only for outdoor use with cold water in gardening and irrigation applications. It has not been tested or rated to be used with warm or hot water.
MNPT stands for Male Nominal Pipe Thread
greg, this swivel is for outdoor irrigation use with cold water only.
Sometimes NPT threads are referred to as MPT ('Male Pipe Thread'), MNPT, or NPT(M) for male (external) threads; and FPT ('Female Pipe Thread'), FNPT, or NPT(F) for female (internal) threads.