Originally Posted by zandoval

No problem. I have silver soldered/brazed many Shifter and Cable Bosses to my steel frames. I use a little Harbor Freight touch and plumbers silver solder with regular copper pipe flux. It's no biggy but you should do a few test runs on similar tubing. I also make sure the frame and bosses are clean and sanded to expose raw metal.

https://framebuildersupply.com/collections/braze-ons