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Pneumatic Automation / Distribution & Conveyance / Push-to-Connect Fittings / Metallic / Brass Fitting
Layer 02 · Distribution & Conveyance Industry Leader · Alkon Emerging · AIGNEP
01What 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.

Compare tiers ↓ How to sell this ↓ Request a quote →
Real-world reference Representative metallic / brass fitting
Metallic / Brass Fitting — representative product photo
02Why it's needed

Why this matters.

Tips and pointers on when brass PTC is the right call — and when to spec something else. Scroll the strip →

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.

03Key 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.

01 · Input
Measure the existing tube with a caliper — the fitting OD must match exactly. 6mm = 0.236", 1/4" = 0.250" — the 0.014" gap leaks indefinitely. Metric and inch are not interchangeable.
Metric: 4mm · 6mm · 8mm · 10mm · 12mm · 16mm · Inch: 1/4" · 3/8" · 1/2"
02 · Input
The matched tube on a brass install. Critical: PU caps at ~145 PSI — a 200 PSI brass install on PU blows the tube off, not the fitting. Spec nylon (PA) for the pressure.
PU (≤145 PSI clean air) · Nylon / PA (≥150 PSI — brass default) · PE (utility runs)
03 · Input
Read the component port spec sheet. NPT/BSPT seal on the threads (sealant required); BSPP seals on a bonded washer at the shoulder — no thread sealant. Cross-threading creates immediate failure.
NPT: 1/8" · 1/4" · 3/8" · 1/2" · BSPT / BSPP: G1/8 · G1/4 · G3/8 · Metric: M5 · M10 · M12
04 · Input
Pull from the connection geometry at the install point.
Straight · Male / female straight · Elbow (90°) · Tee · Y · Cross · Reducer · Bulkhead · Plug / cap
05 · Input
Default to nickel-plated for any humidity, chloride, or oil exposure. Plain brass only in dry indoor service — and there, composite is usually cheaper.
Nickel-plated brass (default — oily / humid / outdoor) · Plain brass (dry indoor only) · Fully-metallic, no polymer sleeve (made-to-order, MOQ + lead time)
06 · Input
Drives the spec step: above 150 PSI sustained, above 140°F, or any oil/coolant exposure rules out composite and forces brass.
High pressure (150-230 PSI) · CNC / coolant-mist · Hot-side compressor room · Outdoor / humid · Standard indoor
07 · Input
Number of pieces. Multiple sizes? Add separate quote lines per size variant. Problem-machine re-spec lands at 8-20 fittings; full plant retrofit 50-200+.
1-10 pcs · 25-100 pcs (counter stock) · 500+ pcs (volume tier)

Need different sizes, colors, or quantities? Fill the form, add to quote, then fill again — each click is one quote line.

04Choose your solution tier  ·  core differentiator

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

Most distributors sell one brand per product type. SPC's 60-brand portfolio means every Product Type page surfaces three real options matched to how your customer is buying today. Pick the tier; the quote desk handles the cross-reference.

01 Industry Leader 1 brand
Alkon
Alkon brass push-to-connect fittings
View brand →
02 Emerging 1 brand
AIGNEP
50000 Red / Black metallic push-in series; 57000 heavy-duty nickel-plated brass series
View brand →
05How to sell this  ·  distributor talk track

The tier conversation closes the deal. The cross-reference catalog wins the next one.

When a customer's composite fittings keep failing on the same drop, the answer isn't a better composite — it's the brass upgrade for that drop. Diagnose, re-spec, sell the install once, end the call-backs.
The SPC difference · how distributors actually buy

The 30-second positioning

The metallic / brass sale is almost always a diagnostic conversation, not a catalog conversation. Three questions resolve most quotes: what's the operating pressure (anything sustained above 150 PSI rules out composite); what's the operating temperature (above 140°F rules out composite); what's the environment (oily, coolant-mist, humid, or outdoor rules out composite). Any one of the three tips the spec to metallic. All three together make it non-negotiable.

Tier: Industry Leader tier — nickel-plated brass, stainless grab-ring, full thread coverage (NPT, BSPT, BSPP, Metric), full configuration coverage, deep US stock. The volume play for MRO and general machine builds. Emerging tier is the European engineered-system pick where the customer is standardizing fittings, valves, cylinders, and FRLs on one brand. Economical tier is the US-domestic value play on bread-and-butter NPT-thread inch-tube installs.

Bundle the matched tubing. A brass fitting at 200 PSI demands nylon (PA) tubing rated for the pressure — PU caps out around 145 PSI and blows the tube off before the fitting fails. Quote the matched nylon on every brass quote.

Stocking pattern: a problem-machine re-spec is rarely "one elbow." It's 8-20 fittings on the affected drops, plus matched nylon tubing, plus PTFE thread sealant. A $400-$1,500 single order that stays installed for years.

Customer cue → talk move

"Composite fittings keep leaking on this machine"
Diagnostic first. Pressure above 150 PSI? Re-spec the failing drops to Industry Leader tier brass + matched nylon. Frame as "one-time fix" vs. six-month replacement cycle.
"Need fittings for 200+ PSI line"
Composite is off the table. Industry Leader tier for engineered builds, Economical tier for US-spec NPT inch-tube where price matters.
"Building a CNC cell with coolant mist"
Don't even quote composite. Coolant aerosol plates every surface and softens technopolymer at the O-ring seat. Quote nickel-plated brass for the whole machine's connection layer.
"Spec says no polymer anywhere"
Route to the separately-sourced made-to-order fully-metallic channel. Confirm MOQ and lead time before quoting.
"Standardizing on one European brand"
Emerging tier. Matched system: fittings, valves, cylinders, FRLs share thread standards and mounting.
"Brass but unsure on plating"
Default to nickel-plated. Plain brass corrodes in humidity and any chloride exposure. Plain brass is only the right call in dry indoor non-oily service — and there, composite is cheaper.
Request a quote → Back to tier compare ↑
06Where 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 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

09Install · 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.
10Troubleshoot · 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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