3/8 inch Black Iron Coupling Female x Female

3/8" Black Malleable Iron Coupling – Threaded Fitting for Schedule 40 Steel Pipe

The 3/8" black malleable iron coupling is a straight inline fitting designed to connect two sections of male-threaded steel pipe in low- to medium-pressure systems. Manufactured in accordance with ASTM A197 and ASME B16.3 standards, this full coupling provides a threaded connection that is secure, durable, and suitable for a range of non-potable mechanical piping systems.

This fitting is typically used in gas, air, oil, or steam distribution lines where Schedule 40 black steel piping is specified. The interior threads conform to ANSI B1.20.1 standards for tapered pipe threads, facilitating a tight mechanical seal when used with compatible components and approved thread sealant materials.

Product Characteristics

• ✅ Material: Malleable cast iron per ASTM A197
• ✅ Thread Standard: NPT female x NPT female (ANSI B1.20.1)
• ✅ Nominal Size: 3/8 inch
• ✅ Finish: Black oxide coating – suitable for dry gas or oil systems; not recommended for water unless protected
• ✅ Pressure Rating: 300 psi (WOG); 150 psi (steam) when installed according to code and manufacturer guidelines

Installation Notes

Apply PTFE tape or pipe joint compound to male threads prior to assembly. Coupling installation should avoid over-torquing, which can cause thread distortion or fracture in malleable iron fittings. Use pipe wrenches on adjacent pipe lengths or fittings rather than directly on the coupling to avoid damage to the thread faces or outer wall.

Common Applications

Used across commercial and industrial systems, this coupling is found in natural gas distribution, compressed air systems, mechanical fuel lines, and closed-loop hydronic piping. It is also commonly employed in valve assemblies, branch extensions, and other areas requiring reliable in-line threading within confined spaces.

Material Performance Insight

Malleable iron offers improved tensile strength, shock resistance, and thermal tolerance compared to standard cast iron. Its machinability and dimensional stability make it ideal for threaded connections in rigid mechanical systems that experience thermal cycling, vibration, or pressure variation.