lukus is right. While the micarta rivets are OK strength wise, they are not really there for strength, but for looks. I use them for contrasting, but easy to finish ,rivets in micarta ( and occasionally ivory) handles. The thing that keeps my handles on is good adhesives, and proper glue engineering - allowing a "glue reservoir" by concaving the tang, drilling extra tang holes, using a slow set resin, avoiding excessive clamp pressure. That and the fact that I usually use Corby bolts.
Stacy