Is hole size standardised for window-mounted fans?

[David Peters]

I want to replace an old Xpelair window fan (model FXC6) as it's too powerful. See

believe it's called a "6 inch fan". The blade diameter is 6inches (150mm).

The diameter of the circular hole in the window is 184mm (seven and a quarter inches).

Is this hole diameter standardised so that a replacement "6inch/150mm fan" from BLOGGS & CO would be expected to fit a window hole of 184mm diameter?

[Owain]

This one is a 7 /14 " hole size so probably fairly standard

would adding a speed controller like less work and cost than replacing the fan?

Owain