There are a number of aluminium and steel parts on the car. Some of these parts have bolts, plugs etc that are screwed into it. Unfortunately, when unscrewing or screwing in these bolts, the threads can get stripped. But fortunately, this is an easy fix. The holes can be tapped out and a new bolt can be purchased to fit the new size hole. Very simple. To save having to tap a hole, be very careful when doing up the bolt, especially with aluminium. If this isn't a job you can do, any mechanic will fix it.