I used the 3D printer to print 21 little arrows of varying lengths. These were for an activity I designed and ran at a Scientist Spotlight event at the Museum of Natural History. In the activity, participants used the arrows to slide along gridlines and create mathematical objects called “semigroups.” The original printed arrows were white, but I later painted them in different colors and labeled them, to add some whimsy and help me keep track of which arrows were which lengths.