I have a century hawk pro with and O.S. 37 and I have had a problem with the feathering shaft failing on me. I have been in contact with century on several occasions and they are working with me on solving this problem. The first time it failed on me was when it was assembled from the factory, nothing in the head had been touched. Now if the nut had loosened up I could understand that this wouldnt be an issue but more of my fault because I failed to prepare the model correctly but the nylock nut sheared off the shaft, the threads were flatened. I claimed a bad part with them and they replaced all the damaged parts from the incident and explained to me how to properly assemble the shaft. When the parts were recieved I first greased the shaft and applied lock tight to the threads as instructed and tightened so that the blade grips had freedom of movement and tourqed down according the the thread size on the shaft in accordance with faa publication AC 43.13 1B. After 4 consecutive flights the shaft failed on me again in a hover. The feathering shaft failed in the EXACT same manor as it had in the first incident where I didnt even do anything to it, so that rules out something that i may have done. Upon inspection the threads were again just flatened because the nut just sheared right off of the shaft. ALL of my flights have been performed at 75% throttle....I havent even been to full throttle and this is happening to me. I have been talking to Antonio at helicopter world and we are both baffled at this sittuation and even Adam turner was used to test some shafts to see if they could get them to fail but no luck. has ANYONE else out there had any issues with something like this happening to them, if so please speak up because if this is a manufacturing issue they need to be made aware of it and it will take more than just my claim. If anybody has any insight into this issue please feel free to comment.