This would be a 5-star review, if it wasn't for one thing. Just as stated by several other reviewers, the center nut was coming loose after only 20 minutes of use. I tried to hand tighten on the top, but it came lose again after only a few minutes. Solution: Using a wrench, tighten the top external ring nut (plastic, so be careful), and now its perfect. Used it for an entire day to clean the patio, walkway, driveway, and deck. Works great now. It appears that during assembly, the center nut is o...