When i had a set of tyres recently i found that the centre wheel trims with the ten bolts holding them on had most of the shoulder that the bolts go up against had sheared off. Although all the bolts were there the trim was only secured by 3 or 4 of the bolts. The centre trims are only made of plastic so over the years these had broken but gone unnoticed. I discovered on ebay some 17.5mm internal caps that are stoppers used on test tubes. The ebay number is110902657651. They come in packs of 20 so two packs at £5.00 each will do all the bolts. I punched a hole in the centre, put the bolt in and the shoulder on the stopper fits firmly onto the wheel trim. i also put them on the bolts where the trim shoulder still existed to make every bolt look the same. They are white in colour and when fitted do not look out of place saving me the mega cost of 4 new wheel trims.