Some jobs are a little more intricate than others and require sitting at a workbench to complete. Other times, we just need to take a load off and enjoy a cold one while admiring our work. Either way, Park Tool's Back Rest Upgrade Kit for STL-1. 2 Shop Stool is a kit that will add the STL-3K backrest to the Park Tool work stool, so you can sit tall and proud at how good of a bike mechanic you have become. It comes with everything you need for the upgrade including the backrest, two steel support bars, and hardware. Please note that the previous STL-1 work stools will not accept the STL-3K as it only works with the STL-1. 2.