Hey Giorgio, I haven't used an aminima, but I've always admired the chief designer, and when you originally posted, I looked on the web and saw one or two pics of rods mounted in the camera base. From those, and the manual specs, the screw mounting is 3/8", the short rods that I saw a pic of had machined flats inboard to enable tightening. If your mounting hole/thread on the camera base has been modified then I supose everything changes.
Maybe take a macro pic showing the threaded hole in the base and the threaded end of the rod(s) you have. If something unusual has been done to the base, threads, the a fix may not be too hard for a good machinist or hobyist with a lathe.