Brass 1 1/2" Female NH to 1 1/2" Male NPSH (Hex) Storz Size_4" Rigid Storz The most common fire hydrant

The most common fire hydrant outlet in the USA is 2 1/2 inches with NH / NST threads

Equivalent part number - FM20S15

If your FDC is approx

you probably need this plug

State and Local governments

Brass 1 1/2" Female NH to 1 1/2" Male NPSH (Hex) Storz Size_4" Rigid Storz The most common fire hydrantFemale to male adapters are used to bridge male to female hoses, pipes or valve fittings. Brass is commonly chosen for corrosion resistance, and is popular with chemical or salt water applications. Equivalent part number FM15F15S WARNING: This product contains a chemical known to the State of California to cause birth defects or other reproductive harm. Do not use in connection with drinking water. Wash hands after handling. Brass Female to Male