Bushing, MPT x FPT (Flush Style) PVC Schedule 80 1" x 3/8" (839-129)

This 1" × 3/8" Schedule 80 PVC Flush Bushing provides a compact, all-threaded two-step size reduction from a 1" female-threaded port down to a 3/8" female NPT threaded outlet in a Schedule 80 PVC pressure system. The 1" MPT exterior threads directly into any compatible 1" FPT port — on a tee branch, cross outlet, valve body, manifold fitting, or equipment nozzle — while the 3/8" FPT interior receives any compatible 3/8" male-threaded fitting, valve, instrument isolation component, or manifold connection on the reduced side.

The 1" inlet is what defines the broad application reach of the 839-129 within the 839-series family. One-inch NPT is among the most prevalent threaded port sizes in commercial and industrial piping — appearing across standard valve bodies, pump ports, strainer inlets, process tee branches, manifold fittings, and equipment nozzles throughout industrial and commercial installations. Wherever a 1" FPT port in a Schedule 80 system must interface with a downstream component presenting a 3/8" male-threaded connection, the 839-129 accomplishes that full two-step transition at the port face in a single flush bushing — eliminating the need for an intermediate reducing coupling, a separate 1"-to-1/2" bushing plus a 1/2"-to-3/8" bushing in series, or any other multi-fitting assembly to bridge the two-step size gap.

The 3/8" FPT outlet defines the downstream application niche. Three-eighths inch NPT occupies an intermediate small-bore position — larger than the 1/4" gauge-port standard used for most pressure gauges and transducers, but smaller than the common 1/2" branch pipe size. It appears at instrument isolation valve ports, small-bore instrument manifold outlets, fine-bore chemical injection connections, and select instrument body inlets where equipment manufacturers specify a 3/8" NPT connection rather than the more common 1/4" or 1/2" sizes. When a 1" FPT port in a Schedule 80 system must feed one of these 3/8"-ported components, the 839-129 is the direct, single-fitting bridge between the two sizes.

Within the 839-series 1" inlet sub-run, the 839-129 serves the 3/8" downstream connection requirement — the only outlet size smaller than 1" and larger than 1/4" that might be written in this sub-run. Buyers who need to reduce a 1" FPT port to the more common 1/4" gauge-port standard would require a 839-series entry at 1" × 1/4" if stocked; buyers reducing to a 1/2" downstream thread would require a 1" × 1/2" entry. The 839-129 specifically and exclusively serves the 3/8" downstream requirement at the 1" inlet — a specialized but recurring connection scenario in instrument supply and control system piping where 3/8" NPT ports are specified.

Compared to its closest catalog neighbor, the 839-073 (1/2" × 3/8"), the 839-129 serves a larger upstream port size with correspondingly broader application coverage — the 1" FPT ports on standard Schedule 80 tees, valve bodies, and process fittings are far more common than the 1/2" ports the 839-073 reduces. The trade-off is a lower pressure rating: at 1" MPT the governing end carries approximately 450 psi @ 73°F vs. the ~850 psi of the 1/2"-governed 839-073. Both deliver the same 3/8" FPT outlet for the same downstream instrument and control system connections, but serve different upstream port contexts.

As with all 839-series fittings, the all-threaded MPT × FPT configuration distinguishes this bushing from the 838-series. The 839 MPT end threads into female-threaded ports; the 838 spigot end cements into slip sockets. When the 1" port to be reduced is female-threaded, the 839-129 is the correct selection. The complete assembly — installation into the 1" FPT port and connection of the 3/8" downstream component — is accomplished with PTFE tape and thread sealant in a fully threaded assembly without cement work or cure time at the bushing.

The flush style eliminates the protruding hex shoulder of a standard hex bushing, producing a low-profile, streamlined assembly that installs cleanly inside the receiving 1" FPT port without adding axial projection beyond the port face. In tightly spaced manifold assemblies, valve body port arrays, and equipment nozzle clusters where adjacent fittings limit clearance at each port position, the absence of a hex shoulder preserves the clearance needed to work at neighboring ports without interference from the bushing body at the reduced port.

Manufactured in dark gray Schedule 80 PVC, this bushing delivers the increased wall thickness and mechanical strength required in industrial, chemical, and commercial pressure piping where Schedule 40 ratings are insufficient. PVC's broad chemical resistance covers acids, bases, salts, chlorine, and most common process and instrument fluids, providing long service life in corrosive environments where metal bushings would corrode, seize on threads, or contaminate sensitive instrument supply lines and process connections. NSF/ANSI 61 listing confirms suitability for potable water contact.

Rated to 450 psi at 73°F (governed by the 1" MPT end), this bushing handles the full range of standard to moderately elevated pressures encountered in commercial and industrial Schedule 80 PVC systems. Apply two to three wraps of PTFE tape to the 1" MPT exterior before threading into the receiving port — hand-tighten plus one to two turns using a wrench on the bushing body; avoid pipe wrench engagement on the small bushing body at this size. Apply PTFE tape to all male threads engaging the 3/8" FPT outlet before installing downstream components; 3/8" NPT connections should be hand-tight plus one to two turns — do not over-torque at this small thread size where thread engagement area is limited and PVC cracking risk increases with excessive force. Apply published pressure derating factors for service temperatures above 73°F.

Specifications:

Industries & Applications:

• Instrument Supply & Control System Piping — Reduces a 1" FPT port on a Schedule 80 PVC tee branch, valve body, manifold fitting, or equipment nozzle to a 3/8" NPT connection for instrument isolation valves, small-bore analyzer inlets, and control system components specified at 3/8" NPT in commercial and industrial PVC pressure systems where 1" FPT ports are the upstream connection — the defining application for the 1" × 3/8" size combination across system types where 3/8" NPT instrument components interface with 1" process fittings
• Industrial Process Piping — Provides a compact all-threaded two-step size reduction at 1" FPT branch positions on Schedule 80 PVC process headers, pump manifolds, and equipment connection tees in chemical processing, water treatment, and manufacturing facility piping where downstream instrument isolation valves, fine-bore flow control components, or small-bore branch connections present 3/8" male-threaded inlets at standard 1" process fitting port locations
• Chemical Dosing & Injection Systems — Installs at 1" FPT ports on chemical dosing manifolds, reagent distribution headers, and injection assembly tee branches where 3/8" NPT back-pressure regulators, fine-bore flow control valves, or small-bore chemical metering components must be connected in systems handling acids, caustics, and aggressive process fluids at standard 1" process connection sizes
• Water & Wastewater Treatment — Reduces 1" FPT instrument tap and branch connection ports to 3/8" NPT fittings and valves on Schedule 80 PVC process headers, chemical feed manifolds, pump station piping, and filter vessel instrument branch connections in municipal and industrial water treatment and distribution facilities where 3/8" NPT instrument components interface with 1" process piping ports
• Commercial Plumbing & Mechanical Systems — Provides a two-step all-threaded size reduction at 1" FPT branch outlets on Schedule 80 PVC manifolds, threaded tees, and valve body instrument ports in mechanical room and building utility system piping where 3/8" NPT downstream components — small-bore shutoff valves, instrument isolation valves, or fine-bore branch connections — must be installed at standard 1" FPT port positions
• Irrigation & Agricultural Systems — Reduces 1" FPT branch ports on threaded tees, zone manifold fittings, and distribution valve bodies to 3/8" NPT connections for fine-bore control valves, chemical injection components, and small-bore instrument connections at standard 1" port positions in commercial irrigation headers, greenhouse distribution systems, and agricultural water supply networks
• HVAC & Mechanical Systems — Installed at 1" FPT ports on Schedule 80 PVC cooling tower chemical feed headers, treated water monitoring distribution fittings, and glycol system branch tees where 3/8" NPT valves, meters, or instrument components must be connected at standard 1" process fitting port positions in commercial mechanical system piping