It's 24mm wide. The single pole switch is 12mm wide. See the comparison photo above.
This will fit many pressure cleaners with different part numbers, check out ALT3819620 for a more affordable alternative.
SAFETY WARNING! All electrical parts should ONLY be fitted by an electrically COMPETENT person.
As it's light, maximise the saving on postage and buy some of the related pressure washer parts below. Or some parts for your Nilfisk-ALTO or WAP vacuum cleaner, such as dustbags and the filters or a new floor tool.
At the moment, standard postage within Australia is capped at a maximum of $20!