Ok I've all the information, I will be careful to mount hood after cleaned the flange to avoid any scratch...Only one thing it's dark, if this hood is a press with a clamp, how can screw it in the stepup ring?
I've take a look to your album picture but I still don't understand ...could you send me some (little) picture with a detail, thanks for your patience!!!!

Marco,
I'm leaving town for a holiday here. I will have to take some pictures later. But, the Hama has no screw threads on it. The mounting ring has slits to make it easier to push on over the outside diameter of a stepup ring or the flange on the MX500. There is a toggle clamp that looks similar to a hose clamp for an automobile. You push the toggle down and it draws a band tight around the outside of the hood to keep it affixed to the flange.

Ah ok, I'm going to understand, when you can, I'm very happy if you send me some photos...A friend this holiday goes to Dan Francisco I hope she found these devices so I can save shipping and cost money...

Marco,
I have posted 12 new pictures in the Hama Hood album pages 2 and 3 that show how the locking mechanism fits onto a stepup ring. This is also how it would fit onto the outer flange of your stock hood. Note that you will not be able to use a filter behind the hood if you install it onto the flange of your stock hood.

Really thanks, very very intersting, now I've understand...I think I will order this device...I hope taxes beetween Usa and Italy aren't much expensive...