I must be lucky as all the brass inserts I have pulled so far had a fairly thick bottom end to them, the thread of the machine screw barely makes a mark in the brass but holds strong enough to pull it out of the carb body. I did use a bottoming tap once but found the machine screw to be better to hold and pull the brass valve body out with. I made up a puller that a long nut on the machine screw can thread down the shaft and it applies enough force to pull the brass part out with little effort. Think of a steel bar 1/4" X 1/2" X 1.5 " long with a hole in the middle, thread the screw through the hole and then into the brass nozzle body , the bar spans the carb body resting on the outer rim , then just run the nut down. When it contacts the bar a couple turns with a wrench or pliers and the valve body pops right out undamaged. I found using a new machine screw each time gets a better hold on the valve body, I have lots of them in the screw assortment tray.