Bk Mueller 521-320HC Reducing Coupling 3/8x1/8 in Threaded

Product Description

The BK MUELLER 521-320HC is a black malleable iron reducing coupling designed for threaded pipe assemblies in low-pressure gas, air, and liquid distribution systems. It transitions between a 3/8-inch and 1/8-inch female iron pipe (FIP) threaded connection, making it a standard fitting in branch line reductions and instrument taps. Rated at Class 150 with a 300 psi pressure rating, this coupling handles typical residential and light commercial service pressures without issue. The black finish is standard for gas-service fittings and distinguishes this coupling from galvanized water-service fittings on the job site.

This reducing coupling is used in residential and commercial gas piping, compressed air lines, and general-purpose liquid distribution where a threaded malleable iron fitting is required. Common applications include reducing a 3/8-inch branch line down to a 1/8-inch port for pressure gauges, drip legs, or instrument connections. Licensed plumbers and pipefitters install this fitting per IFGC or IPC requirements depending on the service.

Key Features

• Malleable iron construction provides durability in threaded pipe assemblies
• Black finish identifies this as a gas-service fitting per industry convention
• FIP threaded connections on both ends for standard NPT pipe compatibility
• Class 150 rated at 300 psi working pressure
• Reduces 3/8-inch to 1/8-inch to suit gauge ports, instrument taps, and branch reductions

Compatibility

Designed as an OEM-style replacement or new-install fitting for standard NPT threaded malleable iron pipe systems rated at Class 150 or lower pressure service.

Installation Notes

Installation should be performed by a licensed plumber or pipefitter in accordance with applicable IFGC or IPC code requirements. Shut off and depressurize the line before removing or installing any threaded fitting. Apply an approved pipe thread sealant or PTFE tape to the male threads before assembly. Do not over-tighten; hand-tight plus a wrench-turn appropriate to the pipe size is standard practice for malleable iron fittings.