I drive a 2002 Skoda Fabia estate. My friend is in the process of rebuilding a crash-damaged Y-reg Polo. As he needs three new steel wheels for the Polo and I need a new spare for my car (both 14-inch), we agreed to jointly purchase a set of four. All made sense until we discovered that the Fabia wheels take five nuts, while the Polo wheels take four. Bearing in mind that these cars are closely related, what's the reason for this difference?