Those cage nuts from Carello are not only to be found on the Giulietta buckets.
Many other and later Carello buckets had them. ( ... even cage nuts on some Siem buckets had the same Alfa number.)
I have Included some pictures of them sitting on a bucket of a Giulia gt (picture 1) from the seventies and on 136mm light buckets for Fiat and or Lancia ( picture 2).
Can you confirm the measurements that I could take ?
Outside diameter of the nut is about 9mm
Outside diameter of the cage is about 10 mm.
Fwiw, here the Alfa and Carello parts number of the little beasts:
Alfa : 101.00.65.010.00/02
Carello 00.532.677 and later 90.000.622
Regarding the numbers you have to know that there was another system of 'shoving' nut used by Carello but that had the same reference in the catalogs. ( Just for making things easy probably!)
Another option, I think that you could use the plastic nuts as on the later Alfa buckets, by cutting the part of the plastic that you donít need, see last pictures.