fitting a bath fan

[vw754]

hi,im getting this fan - Google "ebay.co.uk/itm/EXTRACTOR-FAN-SHUTTER-TIMER-HUMIDITY-SENSOR-150mm-M-/390012449692?pt=UK_Home_Garden_Hearing_Cooling_Air&hash=item5ace8db39c"

the sizes are all at the bottom (please scroll down) currently i have an airbrick in the bathroom wall,ive measure it and its exactly 6"x8" (6"down 8" across) i think it may be slightly big for the screws to fit ,am i right? if so how and what is the easyist way i can pack it to make the fan fit?

(saves me getting another hole cut,when ones already there)

[welsh brickie]

you can wedge it in position and spray expanding foam around it to fix it.