This is a 1/2 inch (0.500) socket exteion holder for a three piece set of varying lengths. Two cutouts on the bottom (26 mm x 20 mm x 4.9 mm) allow for common ceramic magnets to be glued in, which help to keep the exteio in and provide some attraction of the holder to a metal drawer. You'll need to print with supports that are removed for those holes. There are two cradle sizes provided, small and large. Print whatever combination of three you need, and just press fit them into the slots on the base. (Make sure to push down on the center of the cradle to not break the sides). My longer exteion in the picture had a smaller diameter than the other two. I wanted to test this design before posting, and have used it in my garage toolbox for over a year now without issue.