Originally Posted by urbanknight

3-4 threads is not a terrible concern, but it means fewer threads are engaged in the nipple. As mentioned above, it's not a safety issue. You might have a spoke pull out of the nipple and have to either replace it or scrap the wheels, but they're not all going to fail at the same time and take you down or anything. If you want, you can have them rebuilt with nipples that are 2mm longer. I would feel safer with that (and that's what I did with a recent build where the spokes came up a little short), but I've seen wheels with a few threads showing hold up just fine for a long time.