cooker hood installation

[kally]

hello ive just fitted a second hand kitchen in a friends house its almost complete but for the fitting of the extractor ive saved a space and it fits in great but as i never took it out from the other house i cant see how the unit stays in place the only way i can imagine is that its screwed to the 2 units either side i can see no other way. my question there fore is...
is this a safe and normal way of fitting a hood as it does have what i can only describe as pre drilled holes in the hood sides so as to fit to a unint thanks

 

[Diyisfun]

Has it got key hole slots in the back, ie fit 2 screws lift on & then lower. My Hotpoint hood was fixed through the top (remove filter). or as you say fix through the side.