I recently put a set of Fremont black fluorocarbon strings on one of my tenor thinline ukes, and a set of Worth brown fluorocarbon on another one of them. In both sets, with one hanging on the wall for a couple of weeks, and one I used last week that I left in the case, the E string broke. I've used Martin clear fluorocarbon before and that never happened. I have enough extra of both those E strings to replace them, but if it happens again, I might just go back to Aquila, maybe Super Nylgut.