Turns out the strut housings I have are not the original Fiat's. They have a threaded nut at the top and look very much like the early factory ones. But when I started checking the dimensions and comparing them to the ones Greg posted, I realized mine are slightly different. Then it dawned on me, they are the early style of KYB complete replacement strut assemblies. At one time KYB offered two options; replacement inserts that fit the stock housings with removable innards (which is what I previously thought I had), and a complete unit with their own housing and the same insert. Those are what mine actually are. And the dimensions differ from the factory housings. They are slightly narrower and do not have the enlarged diameter section at the top (straight all the way up). I will need to get some more accurate measurements, but initially it looks like maybe the Koni inserts being discussed will not fit inside these.
Interestingly they are the same basic dimensions as Koni housings for the X, except for the top portion. Koni struts also get larger in diameter at the top with a wider nut, like the factory ones have, but Koni housings are actually slightly narrower than the stock ones. They do not use a insertable cartridge but separate internal components (similar to the early factory ones).
