Ruger barrels with this threaded stud for the ER housing retaining screw to thread into, are usually referred to as studded barrels. Ruger quit using studded barrels since ~1983.
Currently Ruger replaces studded barrels with the current non-studded barrels when barrels are sent back for stud repair.
Ruger called their former stud attachments silver brazed, which tells me they used the hi temp silver solder that requires brazing temps.
For those I've resoldered, I used the newer low temp Silver solder from Brownells. Regular solder will not hold!
I use "heat fence" on blued barrels and a pinpoint heat source. Use proper silver solder flux, Tin both surfaces, clamp together, and only play the heat source on the stud. I've been able to re-solder the stud w/o blue damage most every time.