What size screws for mounting ENT electrical box with outer ears
Code is not real specific on the screw size or type but I have seen inspectors flag Sheetrock screws in plastic boxes. why?  Over tightened the plastic can crack on some boxes. I usually use #8 pan /washer style (modified truss is another name I found them under). the wider head secures the box plastic or metal better than a run of the mill screw.
But the reason I started using them is inspectors like them.
I use 3/4” or 1” whatever is cheaper sometimes the 1” are.