Nice wheel, hub adaptor, and horn ring combo pkg. Nice find.
The hub adaptors come in several depts- 1/2" like the one listed by Robert, and 3/4". The one you list appears to be 1/2".
I personally prefer the 3/4" hub adaptors. Any less than this and I found I had interference problems between my hand and the blinker switch arm when I installed the flat steering wheel vs the 1" dished Nardi/recreation wheels.
Good pkg find at for anyone with a Nardi hub wanting to switch over to a more traditional flat wheel and larger P horn button.
Thank you for sharing.