One of my early tools. I think I made this about 15 years ago. Spring loaded centers are mainly used for hand tapping on mills, and drill presses, for anyone who doesn't know. The body has a spring in it, and the center travels straight in, and out. Anyone who has ever tapped a hole crooked, and broke the tap will tell you how great these are. The center loads into the back of the tap handle, and keeps it perfectly vertical. The body I turned, and threaded on an old LaBlond, the center I actually re-purposed from an old grinding center I found in the shops junk box. Tool bit underneath it is 1/4" bit (about 2" long).