I like to cut off a small finishing nail, round the cut end slightly with a file and use it in a slightly countersunk hole (in the inlay). After it is on, you can file/sand flush and it looks pretty neat, but will still hold well. I've also used the tiny wire brads, but what makes me nervous about them is that there is little material left holding the inlay on if you get them truly flush, and it is harder for me to get a neat looking countersunk hole with the brads. One would hold a small one, and 2 would hold almost any size, though if you do it neatly, 4 or even eight could look pretty as well.