Machining Advice Requested

[9W Monighan]

Years ago I worked at a shop that had a continuing job of making button head grease fittings and we had a specially ground tool to groove the spring loaded plunger in the middle of the body. You had to go easy so you didn't break it. Same idea as a semi circular threading tool that can be ground as it breaks and wears. If you're making several this may be an idea to grind yourself a form tool.