Nilfisk-ALTO and Gerni hobby use pressure washer hose machine end adaptor M21 x 1.5mm x 3/8 (250 bar 3,500 PSI)
This screws on to the threaded high pressure M21 x 1.5mm outlet of a hobby use pressure washer. Then a 3/8' hose screws into the 3/8" - 1/4" chrome threaded point. They're no longer available.
Professional pressure washers have an M22 x 1.5mm thread.
Maximise the saving on postage and buy some of the related parts below, such as a hose, filters for your Nilfisk or ALTO vacuum cleaner, or a new floor tool and hose.
At the moment, standard postage within Australia is capped at a maximum of $20!