Parker 391P-6-4 Compression Tube Pipe Coupler Body

Product Description

The PARKER 391P-6-4 is a brass compression tube pipe coupler body designed to connect a 3/8 inch outside diameter tube to a 1/4-18 NPTF threaded pipe connection using a plug-in stem end configuration. Built from brass, this fitting provides reliable sealing in low-to-medium pressure fluid and pneumatic systems. It is rated for a maximum working pressure of 150 psi and operates across a temperature range of 0 to 150 degrees F. The plug-in stem to pipe design simplifies assembly in tight spaces where standard wrench access may be limited. Plumbers, pipefitters, and HVAC technicians commonly install this fitting in compressed air, hydraulic, and fluid transfer lines.

This coupler body is suited for residential and light commercial applications where a compression tube connection must transition to a threaded pipe fitting. Typical installations include refrigeration lines, pneumatic control circuits, and plumbing supply connections that require a secure tube-to-pipe interface. The NPTF thread standard ensures a pressure-tight mechanical seal without relying solely on thread sealant, making it appropriate for systems where joint integrity is critical.

Key Features

• Brass construction for corrosion resistance in fluid and air service
• Plug-in stem to pipe end connection simplifies tube insertion and assembly
• 1/4-18 NPTF thread standard provides a dry-seal, pressure-tight pipe joint
• 3/8 inch tube outside diameter compatibility for common instrument and control tubing sizes
• 150 psi maximum working pressure suits pneumatic and low-pressure hydraulic circuits
• Temperature range of 0 to 150 degrees F covers most ambient and moderate-process applications

Compatibility

Designed as an OEM-style compression fitting for tube-to-pipe connections using 3/8 inch outside diameter tubing and 1/4-18 NPTF threaded pipe ports in pneumatic, fluid transfer, and refrigeration systems.

Installation Notes

Installation should be performed by a licensed plumber, pipefitter, or qualified HVAC technician. Shut off and depressurize the system fully before removing or installing any compression fitting. Inspect tube ends for squareness and burrs before inserting into the plug-in stem; a clean, square cut ensures proper compression and prevents leaks. Verify thread engagement meets NPTF assembly standards and inspect the joint for leaks before returning the system to service.