B K Mueller 521-921HN Black Hex Bushing 3/8x1/4 10 Pack

Product Description

The B K Mueller Industries 521-921HN is a black hex bushing used to reduce a female pipe thread opening from 3/8 inch to a 1/4 inch male thread. This type of threaded reducer bushing is a standard fitting in gas, air, and low-pressure fluid distribution systems. It installs into an existing female-threaded port and accepts a smaller male-threaded component on the outlet side. The hex body allows for wrench engagement during installation. Plumbers, pipefitters, and HVAC technicians commonly use this fitting during new installs, repairs, and system modifications where a threaded size reduction is required.

This hex bushing is suited for residential and light commercial piping applications where a threaded reducer is needed at a junction point. Typical uses include air compressor manifolds, gas distribution headers, water supply lines, and HVAC refrigerant or pneumatic control line connections. The black finish is standard on malleable iron or steel pipe fittings used in gas and air service. Each unit of measure is sold as a package of 10 pieces, making it practical for contractors stocking service vans or shop inventory.

Key Features

• 3/8 inch female NPT inlet reduces to 1/4 inch male NPT outlet
• Hex body design allows full wrench engagement for proper torque
• Black finish suitable for gas, air, and low-pressure fluid service
• Sold in a 10-piece pack for convenient job-site or shop stocking
• Compact, low-profile bushing style fits tight clearances better than a reducing coupling

Compatibility

Designed as an OEM-style replacement or standard-stock fitting compatible with 3/8 inch female NPT to 1/4 inch male NPT threaded piping systems used in gas, air, and low-pressure fluid applications.

Installation Notes

Installation is performed by licensed plumbers, pipefitters, or HVAC technicians following applicable code requirements such as the IFGC or IPC. Shut off and depressurize the supply line completely before working on any threaded connection. Apply appropriate thread sealant or PTFE tape to the male threads per the service medium requirements. Do not over-tighten; use wrench engagement on the hex body and avoid pipe-body contact that could crack the fitting.