I think they had a few different lugs , or at least machined the tapered thread into the lug for a given angle for each size.

Had 2 AlAn's, the 2 ends of the tube were threaded opposite directions I presume , like a turnbuckle ,

so as the tube was rotated it pulled itself into the Lugs at either end.

Being on the wrong side of the Atlantic meant getting the frame back to get what was a pretty cheap repair

as Quoted by the factory in Italy .. was no longer affordable .. air freight priced by Volume more than weight.