Get Connected | Understanding M22 Fittings

M22x14mm vs. M22x15mm Pressure Washer Connections

Pressure washer connections can seem deceptively simple until a hose leaks, a spray gun will not seal, or a new accessory does not fit as expected. One of the most common sources of confusion involves M22 fittings, specifically the difference between M22x14mm and M22x15mm connections.

Although both fittings share the same thread size, a small internal difference determines whether the connection seals correctly or fails. This guide explains how M22 fittings work, why the 14mm versus 15mm distinction matters, and how to properly identify and resolve mismatches.

What Does “M22” Mean?

The term M22 refers to the metric thread size used on many pressure washer hoses, spray guns, pump outlets, and accessories. The “M” designates a metric thread, while “22” refers to the outer thread diameter in millimeters.

M22 fittings are widely used across residential and professional pressure washing equipment and are common in components.

Both M22x14mm and M22x15mm fittings use the same external threads. This is why they will usually screw together without resistance. However, successful threading does not guarantee a proper seal.

Where the Real Difference Is

The critical difference between M22x14mm and M22x15mm fittings lies in the inner diameter of the connection, not the threads.

• M22x14mm uses a 14 millimeter inner diameter Stem
• M22x15mm uses a 15 millimeter inner diameter Stem

Inside the female side of an M22 fitting is an internal sealing component commonly referred to as a stem. This part slides into the bore of the male fitting to create the seal. The stem has a o-ring that seats the adaptor.  This connection type is used at the pressure washer outlet, spray gun inlet, and hose connections.

Why Proper Size Matching Matters

For an M22 connection to seal correctly, the inner diameter of the male bore must precisely match the outer diameter of the female stem. If the sizes do not match, the connection will either leak or fail to assemble.

What Happens When Sizes Don’t Match

• 15mm Stem into a 15mm bore seals correctly
• 14mm Stem into a 14mm bore seals correctly
• 14mm Stem into a 15mm bore will leak
• 15mm Stem into a 14mm bore will not fit

This explains why some connections appear secure when the yoke is threaded together but begin leaking once pressure is applied.

Which Size Is More Common?

Historically, M22x15mm fittings were more commonly used on electric pressure washer outlets and spray guns. Over time, M22x14mm fittings became more widespread due to improved sealing reliability and better compatibility with aftermarket accessories in gas rated pressure washers.

Today, many aftermarket hoses are M22x14mm, 14mm are predominantly used for gas operated pressure washers, while electric pressure washers and thier accessories use M22x15mm fittings.  This mixed usage makes adapters an essential part of many pressure washer setups.

How to Identify Your M22 Fitting Size

The most accurate way to identify your fitting size is to measure the inner bore of a male M22 connection. A 14mm bore will appear slightly narrower, while a 15mm bore will be visibly wider. Product documentation may also specify the internal diameter.

How to Fix an M22 Mismatch

If your pressure washer, hose, or spray gun uses a different internal size, the solution is to use a properly sized adapter.

AR Blue Clean offers such adaptors for sale here:
AR Blue Clean PW554-B, Transfer M22 Swivel Adapter
AR Blue Clean PW553-B, Transfer Adapter

High-quality adapters maintain proper sealing surfaces and unrestricted water flow while preserving full operating pressure.

Common Mistakes to Avoid

• Assuming all M22 fittings are interchangeable
• Forcing mismatched connections
• Ignoring small leaks under pressure
• Replacing hoses unnecessarily instead of using an adapter
• Not Checking the pressure rating of the hose before converting the adaptor

Quick Summary

M22 refers to the thread size, while 14mm and 15mm refer to the internal sealing diameter the "stem". Threads may connect even when seals do not match. If the sizes differ, an adapter is required to achieve a proper seal or your system will leak.

Understanding M22 fittings eliminates guesswork, prevents leaks, and ensures your pressure washer system operates as intended.