Robonova hip and ankle joints
I've got a Robonova RN-1 humanoid robot. It's a great robot but the use of a screws fitted into thin threaded brackets for the hip and ankles is a really bad design flaw in the Robonova.
My robonova's hip/leg joints and leg/ankle joints failed within 2 weeks of building the robot. The joints loosened causing the robot to go off balance and fail many of his moves. The screws eventually came lose. Eventually some of the threaded holes in the brackets wore and became useless!
I've replaced the screws with standard M2 (2mm) screws and matching nuts. The best nuts to use would have been nyloc nuts as they are less likely to come loose. My local fastener supplier was out of M2 nyloc nuts so I had to go with standard nuts (for now :-)).
The advantage of using screws and nuts instead of just screws is that the threads in the bracket holes aren't required so you can utilise all 8 holes (4 threaded, 4 unthreaded) to create an extra strong joint!
Here are some pictures: