Lorica hamata- jointless welded rings

[marcos]

According A. Jouttijarvi  jointless rings are often described as being welded but in the meantime welding  such a small ring is very difficult and therefore those have been  seldom seen, at least in the north Europe and during roman period.
Nevertheless it looks to me a not so rare technique in roman hamatae, I'm pretty sure I saw it previously several times.

Does anyone know which  is the most typical roman technique on making jointless rings? Is the welded one used in roman  times?
I even guess that such a technique disappeared in the middle age, most likely because it is very difficult, but I'm not sure.