BRANDS
Prima Stainless Steel QC Plug 3/8FPT
$15.00
Detail Division · Inspection Report · 56.0081
MTM PRIMA 3/8" FPT Plug
Used on the end of your 3/8" hose threads. A 303 stainless quick-connect plug with 3/8" female NPT threads, machined in the USA to ±0.005" (127 µm). It threads onto any 3/8" male NPT end and snaps into a 3/8" QC coupler, landing its sealing nose in the same spot on the o-ring every time.
LINEAR±0.005"127 µm ANGULAR±1°working surfaces
Part no.
56.0081
Type
Plug (male QC)
Thread
3/8"-18 NPT female
Material
303 stainless steel
Steel origin
Pittsburgh, PA, USA
Process
100% machined, USA
Seal
Nose mates coupler o-ring
Inspection
Digital comparator
01 · Why PRIMA
Built to be the last one you buy
Most pressure washer fittings are made to a price. PRIMA is made to a spec. American-sourced 303 stainless, the precision machining grade, is cut in the USA to ±0.005" and ±1°, deburred, washed, and checked on a digital comparator before it ships.
That engineering shows up in your hand, in the fit, and in the price. You're paying for a fitting that seals the same way on the thousandth connection as it did on the first, and one you shouldn't have to replace.
02 · Drawing
Anatomy of the fpt plug
NOTES
- Material: 303 stainless steel, Pittsburgh, PA.
- Sealing nose mates with the coupler's EPDM o-ring.
- Tolerance unless noted: ±0.005" (127 µm) linear, ±1° angular.
- All edges deburred and beveled.
- Seal with PTFE tape or thread sealant on mating male threads.
Part no.
56.0081
Desc.
3/8" FPT plug
Line
MTM PRIMA
Scale
NTS
03 · Where it goes
How it connects
Threaded end
Any 3/8" male NPT end: a hose end, a gun inlet, or an accessory with male threads.
Quick-connect end
A 3/8" QC coupler. Pair it with a PRIMA coupler for the full tolerance benefit.
04 · Out of the pack
What you'll actually notice
| Standard fitting | PRIMA | |
|---|---|---|
| In hand | Sharp, angular, coarse edges | Beveled and smooth. It almost feels soft. |
| Engagement | Loose, with some wobble in the union | Firm and positive. It takes deliberate force to connect and release, with no slop once seated. |
| Seal | Plug position varies, and water can work around the o-ring | The plug nose lands in the same spot on the o-ring every time |
| Corrosion | Depends on alloy; often brass or unspecified stainless | 300-series stainless. Excellent in water and detailing chemistry. |
05 · Section A–A
Why the seal is repeatable
Schematic · not to scaleLocking mechanism omitted for clarity
Try this before installing: connect a PRIMA plug to a PRIMA coupler and watch the plug seat. The tolerances drive the nose into the exact spot it needs to sit on the o-ring, so there's no room for water to deflect around it. Every connection seals the same way.
06 · Process log
How every fitting is made
OP 10Source
303 stainless from Pittsburgh, PA
PASS
OP 20Machine
100% machined to ±0.005" / ±1°
PASS
OP 30Inspect
Profile verified on a digital comparator
PASS
OP 40Finish
Deburred, beveled, washed
PASSSeal compatibility: read before using solvents
EPDM handles hot water, alkaline degreasers, acidic wheel and mineral cleaners, and most detailing chemistry well. It does not tolerate petroleum-based products.
- Avoid running petroleum solvents, oils, or solvent-based tar removers through these fittings.
- Citrus (d-limonene) degreasers can swell EPDM over time. Rinse after use.
- A swollen or nicked o-ring will leak no matter how precise the fitting is. Replace the o-ring, not the fitting.
07 · Application
Who this is for
Who
Professional detailers, mobile operators, and enthusiasts who are done with leaky, gritty quick-connects
What
A 3/8" FPT Plug in US-machined 303 stainless
When
New builds, or replacing a worn or leaking QC point
Where
Hose ends and accessories where you want the plug half of the connection on a male-threaded fitting
Why
A repeatable, leak-free seal and smooth action, connection after connection
Keep it clean
Tight tolerances don't like grit. Don't drag connections through dirt, and rinse them after each job.
Inspect seasonally
Check o-rings for flat spots, nicks, or swelling. A worn o-ring is the most common cause of leaks.
Replace the seal
The stainless will outlast your machine. Keep spare EPDM o-rings on hand.
08 · Is it worth it?
That's your call
Tighter tolerances mean a lower failure rate most of the time. There's a trade-off, though, and anyone who's run a tight-tolerance firearm knows it: precision parts are less forgiving of dirt. Keep these clean and out of the mud, and they're an upgrade you can feel, not just one you can see on the receipt.
There is no perfect system. Water carved the Grand Canyon, and given time it will go wherever it wants. With stainless, the failure point is almost never the metal. It's a degraded o-ring or a dirty connection. Keep them clean, inspect them seasonally, and these should be the last fittings you buy for that spot on your rig.
09 · FAQ
Common questions
What does a 3/8" FPT plug thread onto?
Any 3/8" male NPT (MPT) thread. The threads are inside the plug's hex body. Seal the male threads with PTFE tape or thread sealant before assembly.
Does the plug have its own o-ring?
No. The seal lives in the coupler. The plug's machined nose is what lands on the coupler's EPDM o-ring, which is why nose precision matters so much.
What's the difference between FPT and MPT?
FPT (female pipe thread) has threads on the inside; MPT (male pipe thread) has threads on the outside. A female fitting threads onto a male end. Both use NPT, the US tapered pipe thread standard, so match the size: 3/8" to 3/8", 1/4" to 1/4".
Coupler or plug: which one do I need?
Every quick-connect union has two halves. The coupler is the socket with the pull-back sleeve and the o-ring. The plug is the solid nose that snaps into it. You need one of each at every connection point.
Why are PRIMA fittings harder to connect than my old ones?
Less clearance between plug and coupler. The firm engagement is the tolerance at work, and it means the union has no room to wobble or let water bypass the o-ring.
Is 303 stainless more corrosion resistant than other stainless fittings?
Not meaningfully. 303 is chosen for machinability, which is what allows the tight tolerances and smooth finish. Its corrosion resistance is excellent in water and detailing chemistry, but the reason to buy PRIMA is fit and seal.
What chemicals should I keep away from the EPDM seals?
Petroleum solvents, oils, and solvent-based tar or adhesive removers. Citrus degreasers can also swell EPDM with repeated exposure. Water-based alkaline and acidic cleaners are fine.
Where are PRIMA fittings made?
Veloci Performance began machining the PRIMA line in the USA in 2023, using 303 stainless sourced from Pittsburgh, Pennsylvania. Detail Division ships them nationally and internationally.
Made in USASteel · Pittsburgh, PA
In 2023, Veloci Performance moved production of a select group of pressure washer fittings to the United States. Material and shipping costs were squeezing the global market, and they saw it as a chance to build something better instead of cheaper. PRIMA is the result: American steel, machined to a tolerance most fittings never see.
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