I think he's referring to the stop pin on a balisong. Those pins are often a weird size, in the neighborhood of 3/32". An old drill bit end will work. It needs to be a tight fit, so once you tap it into place (it should be tight even at this stage), alternately tap the ends to make it thicker. If you have a graduated drill bit set, you could also use it to determine what size to use if you have to buy one to cut up. You can also buy stainless pin stock from knife supply houses, if you know the size. This is a somewhat simplified answer, but will probably work if you're careful. Drills are kind of hard so wear eye protection when pounding on them. Also keep your eye on your handles to make sure the drill stock doesn't wear them too fast. Some machinist supply houses or even hardware stores also sell various sized pins. It is also possible to enlarge the stop pin hole to accomodate a larger pin, depending on how hard the tang got during heat treat.