I have used Echo Weed eaters for years. I am very happy with them. Recently after many years of use one of mine locked up and I purchased an new one. When changing from the 'string' to the 'blade'.. I noticed that when i run it , the reversed threaded nut will tighten SO TIGHT that it prevents my blade from spinning. I have to wonder why? i HAVE NEVER had a problem with my old Echo running the 'star blade" ( 3 point Echo brush blade). Any help with be appreciated. Thanks, Uncle Timmy.