The glass cups we use in our daily lives are all flat-bottomed, and if we need to carry multiple glass cups at once, we need to use a tray to hold them. However, if a regular tray holds too many glass cups, it becomes difficult to stabilize, requiring one to walk very carefully to avoid spillage of liquid or the glasses falling off. It is much more convenient to use these glass cups with sockets at the bottom, in conjunction with a tray that has supports. Even when holding 6 cups at a time, they won't easily fall off, and used cups placed back onto the tray's supports won't slide around either.