Black Iron Fittings

Black malleable iron threaded fittings for gas, steam, compressed air and hydronic heating. Sizes 1/8" through 4", in FIP, MPT x FPT, three-way FPT and flanged configurations.

Black iron is used on gas because it carries no zinc. Zinc coating can shed inside a fuel gas line and the flakes foul controls and orifices downstream, which is why black is the trade default even though a galvanized fitting looks identical on the shelf. NFPA 54 does permit galvanized steel pipe for fuel gas, so the requirement on any given job comes from the local code and the gas utility rather than from a blanket ban.

Threads are NPT and taper — the seal comes from thread deformation, not from the sealant, so the correct engagement depth matters more than how much dope is applied. Use a sealant rated for the medium: standard pipe dope is not approved for gas, where a yellow gas-rated PTFE tape or a listed compound is required.

Tees, couplings, 90° elbows and street elbows, bushings, caps and plugs make up the range.

Predominantly Mueller Streamline.

Thread engagement figures, Class 150 pressure ratings and Schedule 40 pipe dimensions are collected in our black iron reference guide.

Black iron fittings by size: Mueller Streamline part numbers

The most-ordered Mueller Streamline black malleable iron fittings, by size and type. Each part number links to the product page. Reducing tees, reducing couplings, bushings, 45° street elbows and floor flanges are in the full collection below.

See also: black iron pipe and black iron nipples.

For 2" and larger steel pipe in fire protection and HVAC risers, Gruvlok grooved fittings and couplings join pipe without threading or welding.