Guest 3/8x1/4 M Conn

The John Guest 3/8" x 1/4" Male Connector from Reliance Worldwide Corporation bridges 3/8" push-fit tubing to a 1/4" male iron pipe thread, giving installers a fast way to connect water lines to threaded ports on filter housings, valves, and manifolds. It is a staple in residential filtration and reverse osmosis plumbing, where so many components present a tapped inlet or outlet that has to mate with flexible tubing.

One end is a John Guest push-in collet that accepts 3/8" tubing and seals it with an internal O-ring the moment the tube is inserted. The other end is a 1/4" MIPT thread that screws into a tapped port. This combination lets you transition between flexible tubing and rigid threaded connections in a single fitting, avoiding the stacked adapters that add height, cost, and extra leak points to a build.

How It Works

• Connection: Tube x MIPT in a single straight body
• Steps 3/8" tubing down to a 1/4" male thread
• Polypropylene build resists corrosion and won't scale
• Push-fit tube side assembles in seconds, no tools
• Demountable for clean servicing of treatment equipment
• Reusable across repairs and reconfigurations

Male connectors are among the most-used fittings in any water treatment build precisely because threaded ports are everywhere. To install, wrap the 1/4" thread with PTFE tape, hand-tighten it into the port and snug it just past finger-tight, then cut your 3/8" tube square and free of burrs and push it fully into the collet until it bottoms out. A gentle tug confirms the grip, and the O-ring seals the joint automatically. When the line needs servicing, depress the collet and the tube slides free undamaged. The corrosion-resistant polypropylene body holds up to years of contact with treated water without scaling or rusting. For a secure, leak-free junction between tubing and the threaded hardware of your John Guest filtration system, this reducing male connector delivers reliable results.

Keeping a few of these connectors in stock covers a wide range of hookups, since stepping 3/8" tubing into a 1/4" threaded port is one of the most common transitions in point-of-use systems. Paired with the rest of the John Guest range, it lets you build a complete filtration or RO layout from interchangeable push-fit parts that all assemble and release the same simple way.