Solder preforms were made to do the actual soldering. l also used some electrical non corrosive solder flux paste.
The preforms were made by by winding some 0.020 diameter (0.5mm) electronic solder around an 1/8 inch rod.
I put this spring shaped coil on an index card with the card on a hard flat surface and inserted a hobby knife with a #11 blade in the coil and cut the coils apart by pressing down and drawing the knife out. The card protects the edge of the blade and lets the blade cut all the way through the solder. Then I cut a small segment out of each coil with the knife. When cutting the coils apart the blade will expand each coil a bit so the cutout lets the coil close up to be a snug fit around the nipple. Besides a full ring of solder is more than needed to make a good joint.
A small amount of flux is put on the end of the nipple. There is usually some in the lid of my flux container so I just scrape a little of that onto the nipple. Only a small amount is needed. If I can see that I have some on the part that is enough. If I can see it easily then that is too much. The flux makes the nipple end sticky enough that a solder ring will stick to it when the nipple is pressed down into it. I inserted the nipple into the cup and a little twisting motion distributes some flux around inside the cup recess. The solder ring was pressed down to conform to the joint. I find it is easier to do all this with the parts held in my finger before putting them on the fixture. The assembly was then slid onto the fixture.
A small torch was used to heat the bottom of the cup until the solder flowed. If heated from the bottom the nipple is not over heated. Soon as the solder flows into the joint remove the heat and let cool.
Gail in NM