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Which M22 pressure washer fitting do I need, 14mm or 15mm?
M22 x 1.5 is the common pressure washer thread, but it exists in more than one bore, and the wrong bore leaks or will not seat.
M22 is a thread, not a guarantee of fit
Most consumer pressure washer hoses and lances use an M22 x 1.5 connector, a 22mm metric thread with a 1.5mm pitch. Because so many machines share it, people assume any M22 part fits any M22 machine. The thread does match, but the internal bore and the male stem behind it can differ.
The two you meet most are a 14mm bore version and a 15mm bore version. There are also 22mm and 15mm stem variants in circulation. These are not freely interchangeable, and forcing a 14mm stem into a 15mm seat, or the reverse, gives you a joint that leaks or fails to seal on its O-ring.
Telling the bores apart
The difference is on the male end. Look at the central pin or stem inside the M22 nut and measure its diameter: roughly 14mm on one type and roughly 15mm on the other. The nut thread is the same, so measuring the stem, not the thread, is what identifies the version.
If your new hose threads on but weeps or blows off, a bore mismatch is the usual cause rather than a bad seal.
Karcher is a special case
Karcher consumer machines mostly do not use M22 at all. They use a proprietary bayonet connector that clicks and twists rather than threads. If your machine is a Karcher, an M22 adapter kit made for Karcher bayonet is what bridges you to standard M22 accessories.
Check your machine end before buying: a bayonet outlet needs a Karcher adapter, while a threaded outlet needs the correct M22 bore.
Buying the right adapter
State both ends when you order: the M22 bore your machine uses (14mm or 15mm) and the fitting you want on the other side, whether that is a quick-connect, another M22, or a Karcher bayonet. Matching the stem bore is what stops the leak, and a fresh O-ring on the M22 face finishes the seal.
Get the right fitting
Open the HoseFitFinder toolMatch your M22 boreFind M22 14mm to 15mm pressure washer adapter on eBayaffiliateRelated
Sources: Karcher