Mueller Streamline 521-803 Black Malleable Iron Plug 1/2 in

Product Description

The MUELLER STREAMLINE 521-803 is a 1/2-inch black malleable iron square head plug with male pipe threads (MPT) rated to 150 psi. It is designed to close off open pipe ends in piping systems handling lubricant oil, grease, LP gas, natural gas, and steam. The square head profile accepts a wrench for installation and removal, making it practical in tight-access locations. Licensed plumbers, pipefitters, and gas service technicians typically install this fitting in residential and commercial distribution systems where a reliable, pressure-rated pipe closure is required.

This plug is suited for use in low- to medium-pressure piping systems across a range of applications including natural gas and LP gas supply lines, steam distribution, and lubrication systems. The black malleable iron construction holds up to the mechanical stress of threaded assembly and performs across the temperature ranges common in HVAC and gas piping. It is a standard catalog fitting stocked for service, maintenance, and new installation work.

Key Features

• Black malleable iron construction resists mechanical stress in threaded pipe assemblies
• Square head profile allows wrench engagement for secure installation and removal
• Rated to 150 psi for use in gas, steam, and oil service
• Male pipe thread (MPT) connection in 1/2-inch nominal pipe size
• Compatible with LP gas, natural gas, steam, lubricant oil, and grease service

Compatibility

Designed as an OEM-style threaded pipe plug for 1/2-inch nominal pipe size systems in gas, steam, and oil piping applications.

Installation Notes

Installation should be performed by a licensed plumber, pipefitter, or gas technician in accordance with applicable codes such as the IFGC or IPC. Shut off and depressurize the piping system completely before installing or removing any threaded fittings. Apply an appropriate thread sealant or PTFE tape to the male threads before assembly, following the sealant manufacturer and local code requirements for the specific service media. Do not overtighten, as malleable iron threads can be damaged by excessive torque.

Technical Specifications

• Nominal Pipe Size: 1/2 inch
• Connection Type: Male Pipe Thread (MPT)
• Pressure Rating: 150 psi
• Material: Malleable Iron
• Finish: Black
• Head Type: Square Head
• Application: Lubricant Oil, Grease, LP Gas, Natural Gas, Steam

Standard Information

• Brand: MUELLER STREAMLINE
• Manufacturer Part Number: 521-803