Is a Radial Tube Safe in a Radial Tire ?

Dunno, those rivets sure look structural to me. The modular part is the centering ring. Look at the back, they are deformed just like a rivet. IIRC I read how they were made and the 2 halves are in fact riveted together. I see some of the larger ones may be bolted on the back but Im looking at some old *** Chevy II 15X8's and new SBP 15X3's neither have nuts on the back.