Mueller Streamline 521-403 Black Malleable Iron Cap 1/2 in

Product Description

The MUELLER STREAMLINE 521-403 is a black malleable iron threaded cap rated for 150-pound service, designed to close off the end of a female iron pipe (FIP) threaded line. This fitting accepts a 1/2-inch female thread and provides a secure, pressure-rated termination point for gas, air, or other compatible piping systems. Malleable iron construction offers reliable strength and durability in demanding trade environments. Plumbers, pipefitters, and mechanical contractors install this type of cap during rough-in, system testing, and permanent line termination applications.

This cap is suited for residential and light commercial piping installations where a threaded iron fitting is required to cap an open female-threaded pipe end. Common applications include natural gas distribution piping, compressed air lines, and general industrial piping systems. The 150-pound pressure rating makes it appropriate for standard low-to-medium pressure service conditions typical in these installations.

Key Features

• 150-pound pressure rating suitable for standard threaded iron pipe service
• 1/2-inch FIP (female iron pipe) thread for secure engagement on male-threaded pipe ends
• Black malleable iron construction for strength and machinability
• Threaded design allows installation with standard pipe wrenches — no special tooling required
• Produced to exact dimensional specifications for consistent thread fit and seating

Compatibility

Designed as an OEM-style replacement or new-installation fitting compatible with standard 1/2-inch male NPT threaded iron pipe in 150-pound-rated piping systems.

Installation Notes

Installation is performed by licensed plumbers or pipefitters in accordance with applicable codes such as the International Fuel Gas Code (IFGC) or International Plumbing Code (IPC). Shut off and depressurize the affected line completely before installing or removing any threaded cap. Apply an appropriate thread sealant or PTFE tape to the male pipe threads before engagement. Hand-tighten first, then use a pipe wrench to achieve a leak-free connection without over-torquing the fitting.

Technical Specifications

• Fitting Type: Cap
• Material: Black Malleable Iron
• Thread Type: FIP (Female Iron Pipe)
• Pipe Size: 1/2 inch
• Pressure Rating: 150 lb

Standard Information

• Brand: MUELLER STREAMLINE
• Manufacturer Part Number: 521-403