I correct my statement that the retainer can't be screwed down flush with the bucket.
In the picture on the first post, you can see the 3 channels radiating out from the center, that are pressed into the retainer.
These create ridges on the back that ride on the center edge of the bucket, allowing the retainer to rotate when the retaining screws are adjusted.
If you look at the one that runs down from about 1 O'clock, you will see a crease pressed into it from the back when the retainer was screwed down to the bucket.
These (on the others too) will cause problems with adjusting when the assembly is put together correctly unless they are hammered out.
