Minecraft wiki entry for Time-saving_tips, associated text: Right-clicking with the mouse selects half a stack at a time, or can be used to place a single item in a crafting or smelting slot. Using right-clicks wherever possible helps speed up many crafting recipes from steps and slabs to snowballs, because you can split the stacks into roughly equal portions and convert, for example, a stack of 16 snowballs into four snow blocks with just six clicks. Because crafting is such a big part of the game, making good use of the right-click facility is a big time-saver. Right-clicking on an odd stack gives the higher half, but if you want the lower half, right-click again.