Idler bolt size

[kenman1963]

My idler pulley fell off the car today. I went to the autopart store and bought the replacement but it does not come with the mounting bolt. I cannot find the correct size anywhere. My manual doesn't say and 3 different auto part stores do not have a clue. Does anyone know what size I need and can I get it at Home Depot etc ???

1994 ford explorer

thanks