It starts with a rod of 6061 aircraft aluminum. They machine this into a ergonomic pull handle with sculpted curves and two rubber o-rings to ensure a full seal in your oil dip stick tube. Then these handles are powder coated tough in our favorite color; red, so it will look just right in your engine bay.
Next they evaluated materials for the stem. Many dipstick are made from flattened steel, why? Because its cheap and easy, that is not how they do things. Besides, we all know that when you scrape your metal dipstick down the metal tube that you create metal shavings...that is the last thing you need in your oil.