Trying to figure out what this part is.

If this were my carburetor and I absolutely had to remove the jet, I would put a good quality penetrant like aerokroil on the stuck jet. Make sure to remove all plastic and rubber parts from carb body. Then I would heat it to 300-400 degrees F in and oven and try to get the jet moving with an easy out of the appropriate size. These tools have a clockwise spiral to them and flutes that will engage the brass of the jet body. You must tap them into the opening to get them engaged enough to allow the jet to be unscrewed. If you tap them too hard or deep into the jet it will just expand the jet body and make it even harder to remove. Take it easy and don’t ruin the entire carburetor body. Order a new jet of the appropriate size since you won’t want to reuse it after this abuse. Also, this is some sort of air bleed jet since it is inside the CV slide cavity which is an air only area of the carburetor body.