How to make parts parallel in your lathe. Larger 4 Jaw Chucks generally have Tee Slots machined into their front face. Although these are a useful feature, they are often ignored and never used.
One valuable use is to make and install Height Blocks that (after facing), results in a perfect reference point for machining parts that can easily and accurately transferred to other machines for further machining processes.

This is an easily made add-on for any 4 Jaw Chuck with Tee Slots