Bk 521-405BG Malleable Black Iron Cap 1 Inch

Product Description

The BK 521-405BG is a 1-inch malleable black iron pipe cap designed to terminate threaded pipe ends in gas, plumbing, and mechanical piping systems. Each fitting is individually flag tagged and carries the Mueller logo cast directly into the body, confirming manufacturer traceability. The fitting meets ANSI/ASTM A-197 material standards, with dimensions conforming to ANSI/ASME B16.3, B16.14, and B16.39, and threads cut to ANSI B1.20.1. At 0.316 pounds, it is a compact, heavy-duty fitting suited for black iron pipe installations where a secure, code-compliant end closure is required.

This cap is used in residential and commercial applications including natural gas supply lines, fuel oil piping, and general plumbing rough-in work. It is a standard terminal fitting for capping unused branch outlets, service stubs, or temporary line ends during pressure testing. Licensed plumbers, pipefitters, and HVAC technicians routinely install this fitting in both new construction and retrofit work. The fitting ships and is sold individually, making it practical for single-branch service calls or larger multi-outlet rough-in jobs.

Key Features

• Malleable black iron construction per ANSI/ASTM A-197 for strength and durability in high-pressure piping
• Threads cut to ANSI B1.20.1 for reliable, leak-resistant engagement with standard NPT pipe
• Dimensions conform to ANSI/ASME B16.3, B16.14, and B16.39
• Mueller logo cast into fitting body for manufacturer identification and traceability
• Individually flag tagged and 100% inspected and quality tested prior to shipment
• 1-inch size suitable for common branch and stub termination applications

Compatibility

Designed as a standard NPT-threaded malleable iron end cap for use with 1-inch black iron pipe in gas, plumbing, and mechanical piping systems.

Installation Notes

This fitting is installed by licensed plumbers, pipefitters, or HVAC technicians working on threaded iron piping systems. Shut off all gas or fluid supply and relieve system pressure before removing or capping any pipe end. Apply an approved thread sealant or pipe-thread compound rated for the intended service medium before threading the cap onto the pipe. All gas piping installations must comply with applicable local codes and IFGC requirements, including pressure testing of the completed assembly before returning the system to service.

Technical Specifications

• Material Standard: ANSI/ASTM A-197 Malleable Black Iron
• Pipe Size: 1 inch
• Dimension Standards: ANSI/ASME B16.3, B16.14, B16.39
• Thread Standard: ANSI B1.20.1 NPT
• Weight: 0.316 pounds
• Unit of Measure: Each

Standard Information

• Brand: BK
• Manufacturer Part Number: 521-405BG