Pressure Washer Adapters

Pressure washer adapters fix the most annoying problem in this trade: two parts that both work fine but will not screw together. We keep brass, plated steel, and stainless adapters in every common NPT, M22, and garden hose combination at our Gaithersburg counter. Bring the mismatched parts in, or call 301-519-9274 and read us the threads, and we will pull the right adapter before you waste a trip to three big box stores.

How to Identify Pressure Washer Adapter Threads

Nine out of ten adapter mistakes start with a guessed thread. Before you order anything, figure out what you actually have. Most gas machines and their plumbing use NPT pipe thread in 1/8", 1/4", 3/8", and 1/2" sizes. Guns and hoses on consumer machines usually use M22 metric screw connections. Supply side is garden hose thread. The catch is that NPT sizes are named for the pipe bore, not the outside diameter, so a "3/8 NPT" male thread actually measures about 0.67" across. If you measure 7/8" across an M22 fitting, that is normal too. When in doubt, thread the part onto a known fitting at our counter and you will have your answer in ten seconds.

FPT, MPT, and Reading an Adapter Description

Every adapter in this collection is described the same way: one end, then the other. FPT means female pipe thread, the threads are inside. MPT means male pipe thread, the threads are outside. So a 1/2 FPT x 3/8 MPT adapter accepts a 1/2" male pipe thread on one end and screws into a 3/8" female port on the other. Reducing adapters like this let you step a pump port down to hose size, or step a chemical injector up to match a manifold. Write down both ends of both parts you are joining and the right adapter picks itself.

M22 and 22mm Screw Connections

M22 is the metric screw collar on most consumer gun and hose setups. There are two versions and they do not interchange. M22 14mm has a 14mm inside diameter and shows up on most gas machines from brands like Simpson and Generac. M22 15mm has a 15mm inside diameter and is common on electric machines. The gap matters because the seal is made on an internal o-ring post, not the threads. Force the wrong one together and it will thread on, then leak the whole job. Suttner ST-40 and ST-41 screw couplers and plugs, like the ST-40 stainless screw coupler, convert 22mm connections over to standard 1/4" quick connect systems so you can stop spinning collars every time you swap a lance.

Brass, Plated Steel, or Stainless

Brass is the default for cold water and downstream chemical work. It will not rust, it seals easily, and it is cheap enough to treat as a consumable. Plated steel adapters carry higher pressure ratings, usually 4,000 to 5,000 PSI in this collection, and take more wrench abuse, but they will corrode where soft wash mix sits in the threads. Stainless costs the most and shrugs off both bleach and pressure, which is why soft wash rigs end up converting to stainless one failed fitting at a time. A ten dollar stainless adapter is cheaper than one callback for a rust stain on white vinyl.

Common Adapters and Prices

Prices move with metal markets, so treat these as a guide. Availability changes weekly, and one call confirms what is on the shelf today.

From the Field

Two habits will save you real money on adapters. First, stop stacking them. Every adapter you add is two more thread joints that can leak and one more place flow gets pinched. If you find three adapters chained together on your rig, buy the single fitting that does the whole job. We see stacked reducers behind half the mystery pressure losses that come through our door. Second, seal pipe threads and leave o-ring connections alone. NPT joints need two or three wraps of tape or a dab of thread sealant. M22 collars and quick connects seal on o-rings, and tape on those threads just shreds into the o-ring groove and causes the leak you were trying to prevent. Keep a few spare o-rings in the truck. They cost pennies and they end most drips.

Related Collections

• All fittings
• Quick connects
• Pressure washer hose fittings
• Brass pipe fittings
• Stainless steel pipe fittings
• Hex bushings
• Nipple fittings
• Garden hose couplings
• Swivels
• Ball valves

Local to Montgomery County? Stop by our Gaithersburg pressure washer store and match threads at the counter.

Frequently Asked Questions

What thread sizes do pressure washers use?

Most machines mix three systems. NPT pipe thread in 1/8", 1/4", 3/8", and 1/2" on pumps, unloaders, and plumbing. M22 metric collars on consumer guns and hoses. Garden hose thread on the water supply side. Adapters exist to bridge all three.

What is the difference between M22 14mm and M22 15mm?

The inside diameter of the sealing post. 14mm is standard on most gas machines and aftermarket hoses. 15mm shows up on many electric machines. They thread together but will not seal, so check the inside measurement before buying.

What do FPT and MPT mean on an adapter?

FPT is female pipe thread, threaded inside. MPT is male pipe thread, threaded outside. A 3/8 FPT x 1/4 MPT adapter takes a 3/8" male fitting into one end and screws into a 1/4" female port on the other.

Should I use Teflon tape on pressure washer adapters?

On NPT pipe threads, yes, two or three wraps or a paste sealant. On M22 collars and quick connect fittings, no. Those seal with o-rings, and tape debris ruins the seal instead of helping it.

Are brass adapters strong enough for a 4000 PSI machine?

Quality brass adapters handle typical 3,000 to 4,000 PSI work fine. For 4,000 PSI and up, or for fittings that take daily wrench abuse, plated steel rated at 4,000 to 5,000 PSI is the safer pick. For bleach exposure, go stainless.

How do I convert my screw-on M22 gun to quick connects?

Install a 22mm screw plug or coupler adapter, like the Suttner ST-40 or ST-41, on the gun and hose ends. After that, every lance and accessory snaps on and off in a second instead of spinning a collar at every swap.

Why does my new adapter still leak?

Usually a missing or nicked o-ring, tape on a joint that seals by o-ring, or two thread types forced together, like garden hose thread onto 3/4 NPT. They feel close but they are not the same thread. Bring the parts in and we will sort it out.