Pneumatic Automation / Distribution & Conveyance / Push-to-Connect Fittings / Metallic / Brass Fitting

Layer 02 · Distribution & Conveyance Value · AIGNEP

What it is

Metallic / Brass Fitting

A metallic / brass fitting is a push-to-connect fitting with a metal body, most commonly nickel-plated brass, that threads into a port and accepts a pneumatic tube on the push-in end. The body raises the working-pressure ceiling to roughly 230 PSI and the temperature band to roughly -40°F to +200°F, with a stainless-steel grab-ring inside that bites the tube OD under vibration. Nickel plating adds the corrosion resistance plain brass lacks under humidity or chloride exposure. The push-in mechanism (collet + O-ring + release sleeve) is identical to composite, so install discipline transfers directly. This type covers composite-construction metal-bodied fittings (metal body, polymer release sleeve). A fully-metallic fitting with zero polymer is a separately-sourced, made-to-order construction and is outside this type. For 95% of customers asking for "a metal fitting," nickel-plated brass with a polymer sleeve is exactly what they need.

Pictorial Representative metallic / brass fitting

Metallic / Brass Fitting — representative illustration

Real-world reference Representative metallic / brass fitting

Metallic / Brass Fitting — representative product photo

Why it's needed

Why this matters.

When brass PTC is the right call, and when to spec something else. Review the points below.

01 · Key point

It holds at 230 PSI.

Nickel-plated brass body carries working pressure to ~230 PSI and tolerates pressure-spike cycling that cracks composite at the thread root. The fitting for booster-fed drops, pressing operations, and high-pressure clamping.

02 · Key point

It tolerates oil and heat.

Temperature band -40°F to +200°F; coolant mist and oil aerosol don''t soften the body. CNC machine tools, hydraulic-adjacent pneumatics, hot-side compressor-room runs.

03 · Key point

Stainless grab-ring inside.

Stainless-steel grab-ring (not plastic collet) bites the tube OD firmly and holds under vibration for years. Same push-in mechanism as composite, no new technique for the install tech.

04 · Pro tip

Default to nickel plating.

Nickel-plated brass for any humidity, chloride, or oil exposure, the standard US-market spec. Plain brass only for dry indoor service (and there, composite is usually cheaper).

05 · Where not to use

Washdown, dairy, chloride spray.

Nickel plating is corrosion-resistant, not corrosion-proof. → Step up to stainless-steel PTC for CIP/SIP, marine, coastal, or audit-driven food-contact zones.

06 · Where not to use

DOT truck brake circuits.

Industrial brass PTC is not legal in FMVSS-regulated air-brake lines. → Switch to DOT air-brake fitting on any service, emergency, or parking-brake circuit.

07 · Where not to use

Hard tube (stainless, copper).

PTC seats on soft tube only, the grab-ring won''t bite rigid tubing. → Use instrumentation stainless tube fitting (double-ferrule) for hard-tube instrumentation, gauge, and sample lines.

Key selection criteria

What we need to spec it right.

From the machine spec sheet to the part number. Answer what you know, leave the rest blank, and send.

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Whatever your lever — performance, value, or price — SPC has the right brand.

Pick the priority; the quote desk handles the cross-reference.

02 Value 1 brand

Where it's used

Industries served.

Each industry below uses this product across the listed areas. Open an industry to see how it fits the rest of its system.

Metalworking & Fabrication →

CNC machine tools and machining centers (coolant-mist exposure)

Also applies to High-pressure pneumatic lines (150-230 PSI) · Compressor room hot-side air-prep (downstream of aftercooler) · Hydraulic-adjacent and oil-mist pneumatics · Outdoor and semi-protected installs (variable humidity) · Heavy-industrial OEM machine builds · Distributor service trucks and field MRO

Install · 6 critical steps

The things that matter on the first install.

Step 01

Confirm tube OD, tube material, and pressure rating match the fitting

6mm and 1/4" are NOT interchangeable (0.014" gap = slow leak). PU tubing tops out at ~145 PSI; a 230 PSI brass install needs nylon (PA) tubing. Mismatched tube/fitting pressure ratings blow the tube off, not the fitting.

Step 02

Cut the tube square and deburr the OD

Use a tube cutter (rotary or shear), not side cutters or a hacksaw. An angled cut prevents the O-ring from sealing against the tube OD. Deburr to remove cut marks that would tear the O-ring on insertion. Nylon is harder than PU and demands a clean square cut.

Step 03

Insert the tube to full insertion depth and tug-test

Push straight in (no rotation, no rocking) until it bottoms against the internal stop. Typical insertion depth: 16-22mm. Tug back to verify grab-ring engagement: firm resistance, zero tube travel. Any movement = not seated; it will blow off under pressure.

Step 04

Apply thread sealant by thread type

NPT/BSPT (tapered): 2-3 wraps PTFE tape in the direction of engagement, OR thread paste rated for compressed air, never both. BSPP (parallel): seals on a bonded washer at the shoulder, no sealant on the threads. Sealant on a parallel thread is a leak waiting to happen.

Step 05

Torque to spec

Typical NPT torque: 12-22 ft-lb depending on size. Over-torquing cracks the brass body at the thread root; under-torquing leaves a slow thread leak. Rule of thumb on field MRO: "snug plus 1¼ turns past hand-tight" for NPT. Stop the moment the wrench resists, brass cracks before it groans.

Step 06

Pressurize gradually and soap-test

Bring pressure up in stages (50 / 100 / 150 / full operating) and brush soap solution at every collet, every thread, every release sleeve. Zero bubbles = working. Any foam = real leak; depressurize and address. Most first-start leaks are angled tube cuts at the collet or wrong sealant at the thread, both five-minute fixes.

Troubleshoot · top failures

Most returns trace to one of these causes.

Symptom

Most likely cause

Fix

Slow leak at the collet (push-in end) of a newly-installed brass fitting

Angled or burred tube cut, tube OD scratched (O-ring damaged on insertion), tube not bottomed against the internal stop, or wrong tube OD for the fitting (1/4" tube in a 6mm fitting, 0.014" undersized).

Pull the tube (press the release sleeve fully forward, pull tube straight back). Cut off the affected section with a tube cutter, deburr, re-insert. A brass fitting will not adapt to an out-of-spec OD the way composite sometimes does; verify with a caliper.

Thread leak at the NPT/BSPT port end

Insufficient or wrong sealant (paste used where tape is spec'd or vice versa), under-torqued, or cross-threaded on initial install.

Back the fitting out, inspect threads on fitting and port. If clean, re-apply sealant (tape OR paste, not both) and torque to spec. Visibly damaged threads = fitting scrap + port chase or re-tap. Never over-torque to "stop" a thread leak, that cracks the brass body.

Tube blows off the fitting under pressure

Tube not fully seated past the grab-ring (most common), tube pressure rating below operating pressure (PU on a 200+ PSI line), or wrong tube OD.

Confirm tube is rated for operating pressure, PU caps at ~145 PSI; nylon (PA) required for ~230 PSI brass. Re-seat fully and tug-test. If a properly-rated, properly-seated tube still blows off, verify the fitting source against authorized distribution, counterfeit fittings are a real failure mode.

Brass body cracked at the thread root

Over-torqued at install (single most common cause), repeated thermal cycling on an over-torqued fitting, or impact damage.

Replace. On reinstall, torque to manufacturer spec (typically 12-22 ft-lb) with a torque wrench on machine builds. Multiple cracks on the same machine = install protocol is the root cause; retrain on torque spec.

Nickel plating discolored, peeling, or pitted within months

Plain brass installed where nickel-plated was needed (corroding through), chloride exposure (washdown, coastal humidity, road salt), or sustained oxidizing chemistry.

Verify the fitting is genuine nickel-plated. If chloride or oxidizing chemistry is the driver, nickel-plated brass is corrosion-resistant, not corrosion-proof: re-spec the affected drops to 316L stainless.

Fitting "leaks intermittently", sometimes seals, sometimes doesn't

O-ring seat damaged by oil/solvent (swelling and shrinking as conditions change), or temperature cycling crossing through the 140°F-200°F band where a composite installed by mistake fails intermittently.

Confirm the fitting is actually brass (not a composite the customer thinks is brass). On oil/solvent exposure, FKM replacement O-rings are available on most Industry Leader and Emerging tier lines.

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