Advice on brake re-fitting.

Hi,

I've successfully dismantled my front and rear brakes and managed to somewhat change the components out for new ones.

However I still have a few slight issues. One being that one of the screws which hold your disc brake on to the hub has corroded and consequently become stuck inside the threaded hole on the hub. I have drilled the screw out, but there is still material in the threads, and re-tapping seems out of the question.

Is this screw really necessary as surely the bolts and caliper do the main job of holding the disc in?

Thanks in advance. 

not necessary,but line disc up with hole when re-fitting.