I'm taking the alloys off for the winter and putting steelies on. As I have wobbly bolts on the alloys I need some other bolts. I know the bolts are M12 x 1.5 but what length is best? Will 24mm thread be ok?

Also anyone recommend a good place to buy standard bolts? Local scrappy wants £25 for 2nd ones and ebay about the same. Wheels only cost a fiver to buy!