Wheelsmith fatigue tested 76 spokes 68 of them broke at the elbow and 8 of them broke at the threads. They also came up with a formula that relates stress to life the math will be at the bottom. If wheelsmith's test applies to the real world an if I did the math right then a 2.0mm spoke will last 2.01 times as long as a 1.8mm spoke and a 2.34mm spoke will last 2.84 times as long as a 2.0mm spoke. How much longer will a spoke longer will a single butted spoke last compared to a plain spoke? The problem is wheelsmith combined the two types of breaks into one formula but it looks like a 2.34mm/2.0mm spoke is effectively as strong as a 2.34mm plain spoke. Here is the formula Log(stress)=-.3xLog(cycles)+4.12 all logs base 10 the stress is in megapascals. For a given stress the formula gives the number of cycles where half of the spokes fail. The Log of the stress forms a normal distribution with a standard deviation of .072 and the Log of the cycles forms a normal distribution with a standard deviation of .24