Merit Brass K619-64 Pipe Locknut 4 in 316 Ss Fnpsl 150 Psi

Product Description

The MERIT BRASS K619-64 is a 4-inch pipe locknut manufactured from 316 stainless steel, designed to secure threaded pipe fittings in place and prevent loosening under vibration or pressure. The female national pipe straight locknut (FNPSL) end connection provides a straight-thread engagement suited to locknut applications. Rated at 150 psi, this locknut measures 5-5/32 inches in length and weighs 1.71 pounds. It is installed by licensed plumbers and pipefitters working on industrial, commercial, or marine piping systems where corrosion resistance is a primary requirement.

This locknut is used in piping assemblies that require a secure, non-tapered threaded connection at a panel, bulkhead, or vessel wall. The 316 stainless steel construction makes it well suited for environments exposed to chlorides, salt water, or caustic media. Typical applications include marine plumbing, food processing equipment, chemical handling systems, and other corrosive service conditions where carbon steel or brass fittings are not acceptable.

Key Features

• 316 stainless steel construction provides superior corrosion resistance in harsh and chloride-rich environments
• FNPSL (female national pipe straight locknut) end connection for straight-thread panel or bulkhead mounting
• 150 psi pressure rating suitable for general-purpose liquid and low-pressure piping service
• 4-inch fitting size with a 5-5/32-inch length to accommodate standard panel thickness and pipe engagement
• Single-piece solid construction with no seals or inserts to degrade over time

Compatibility

Designed as an OEM-style replacement or new-installation locknut for 4-inch straight-thread pipe fittings in 150-class stainless steel piping systems.

Installation Notes

Installation is performed by a licensed plumber or pipefitter. Depressurize and drain the system completely before removing or installing any threaded pipe fittings. FNPSL locknuts rely on a straight thread engagement and a mating gasket or O-ring at the panel face for sealing — do not use tapered pipe thread sealant on straight-thread connections. Torque to the fitting manufacturer's specification using a proper pipe wrench or spanner to avoid galling the stainless steel threads.