Drive Centre Insert
Size is the Diameter of the Spur Ring
Usually, when you are doing both spindle work and turning bowls at the same time it's necessary to switch chucks between operations. Not with this drive center insert. Once installed in your chuck, its spring loaded center and multiple teeth are a big help for all skill levels of turners. The center locates your work and presses in as your tailstock presses the work against the teeth. The point does not penetrate too deeply which decreases the chance of splitting and the teeth keep things from drifting.
This particularly nice with hard woods where one would typically need to sink the center in more deeply.