NASCAR Racing: number of cars starting race, number 43, richard petty

Question
why do they have 43 cars to start race regardless of qualifying? how did they pick the magic number, 43

Answer
I call it the Richard Petty rule. The field kept getting expanded until it eventually reached 42 cars. As the King's career wound down all of a sudden he was having trouble making the field. The Petty fans were in an uproar and began staying home (this was prior to "sold-out" races) when he didn't make the race. So NASCAR added the "Past Champion" provisional, a way to get RP in the field and keep the fans coming to the race.