Here is the identification of the AlKo axle and the detailed nut and screw on the swing arm .The screw is Allen ...
https://www.fiatforum.com/gallery/showphoto.php?photo=133654
https://www.fiatforum.com/gallery/showphoto.php?photo=133655
I´ll have to know how it works...
Look that the talbotoc link I sent earlier.