So why don't we use Flexloc nuts? These things often don't have fully rational answers. When they're not critical it's probably a combination of the following: Because the factory don't. Because they aren't widely available. (Chicken and egg argument.) Because we/ they/ others use Nyloc nuts for other purposes. Because the cost of doing the comparison experiments isn't worth the knowledge gained or the consequent advantage. (See the waterless coolant thread.) Are they more expensive, even though the total cost is low?Jonathan PS: There are some interesting observations in the Chapman literature about how he thought about was critical, and innovated enormously in those areas, and what wasn't, and didn't bother in those, regardless of tradition. PPS: Small gains can, of course, be much more important in competitive sport and aerospace applications.