. ..Only go 1/2 size and if the metal is well annealed perhaps
a full size but no more than this or you may cause problems.
On the subject of using a ring stretcher, the only reason I
purchased/used one was because I had a size 12 wedding band with
milgrain edges that had to go up 1/2 size. The chances of me
adding metal and creating invisible joints was highly unlikely
due to the milgraining. I usually size rings up by the addition
of metal, even if I am only increasing slightly. I try to treat
"stretch" as a dirty word...just personal preference.