Well, that plan didn’t last long. Think I’m going scrap the copper extension and just go close. Simpler.
To do this, I’m just cutting off pipe end not the threaded end. I’ll sand down any stick up on other side once installed. The slight lip helps to center in hole and I’ll probably wrap the brazing metal around it.
Nice fit.
Plan is to cut a ring of stay-silv 45 or 56, flux with white paste and evenly heat around the fitting and it should bond nicely.
You can use other brazing materials as well (like coated bronze rods) - but ideally have some silver content to help flow. Silicon Bronze braze would also work well - either tig or gas braze - maybe mig. You could solder it on as well, but you need the right flux to join to stainless - an acid based flux would work.
@KSiegel Pro Table Build Pics - #148 by KSiegel did something similar with a 1" Stainless nipple and tig welded it - that is probably the most reliable method of doing this. This braze method could be done with propane if no tig setup. You just need to make sure you have correct braze metal and flux.