Not sure what you are asking, is it the distance from the hole to an edge, or the distance from the bottom of the hole to the other side of the metal. For AF of pipe fittings have a look at standard parts, at your pressure air fittings are more than adequate. For the alternative question, assuming pressure from the inside on solid metal towards the hole, it will depend on hole size and I am sure some one here can give a guide or the correct formula.