Bk 521-403BG Malleable Black Iron Cap 1/2 Inch

Product Description

The BK 521-403BG is a 1/2 inch malleable black iron pipe cap designed to terminate open pipe ends in gas, steam, and general plumbing piping systems. Manufactured from malleable black iron conforming to ANSI/ASTM A-197, this cap meets dimensional standards ANSI/ASME B16.3, B16.14, and B16.39, with threads cut to ANSI B1.20.1. Each fitting is individually flag tagged and 100% inspected and quality tested before leaving the facility. The Mueller logo is cast into the body of each fitting, providing a reliable indicator of inspection traceability. Plumbers and pipefitters install this cap as a permanent or temporary pipe end closure.

This cap is suited for residential and light commercial piping applications where a threaded black iron closure is required. Common uses include capping gas supply branch lines during rough-in, closing unused tee outlets, and protecting open pipe ends during system pressure testing. The 1/2 inch threaded fitting is a standard size widely encountered in natural gas distribution, steam, and hydronic heating systems. Installation is performed by licensed plumbers or pipefitters following applicable code requirements.

Key Features

• Malleable black iron construction per ANSI/ASTM A-197 for strength and durability in gas and steam service
• Threaded to ANSI B1.20.1 for consistent, leak-resistant NPT thread engagement
• Dimensions per ANSI/ASME B16.3, B16.14, and B16.39 for OEM-style fitment
• 100% inspected and quality tested; individually flag tagged for traceability
• Mueller logo cast into fitting body as an identification and quality mark

Compatibility

Designed as an OEM-style replacement or new-installation fitting for 1/2 inch NPT threaded black iron piping systems used in gas, steam, and general plumbing applications.

Installation Notes

This fitting is installed by licensed plumbers or pipefitters. Shut off and depressurize the piping system completely before removing or installing any threaded fittings. Apply an approved pipe thread sealant or PTFE tape to male threads before assembly, following the pipe compound or tape manufacturer's instructions and applicable local code requirements such as the IFGC or IPC. Do not over-tighten, as malleable iron fittings can crack under excessive torque.

Technical Specifications

• Material: Malleable Black Iron
• Pipe Size: 1/2 inch
• Thread Standard: ANSI B1.20.1 (NPT)
• Material Standard: ANSI/ASTM A-197
• Dimensional Standards: ANSI/ASME B16.3, B16.14, B16.39
• Weight: 0.127 pounds
• Sold As: Each

Standard Information

• Brand: BK
• Manufacturer Part Number: 521-403BG