Heat, It is silver soldered on. It is very critical to install the new one properly for correct timing. It is too cheap to have Dans 40X to do it. He is a member of this forum and really understands timing and tig welds the handles on.
Butch
You can thread the Rem bolt handle w/o removing it from the bolt body. This has been covered on a number of the gunsmithing forums. 5/16-24 seems to be the most popular thread chosen.