Minecraft wiki entry for The_second_day, associated text: To fix a tool, put two damaged tools of the same type and material in a grindstone or your crafting grid. This combines the two old items into a new item that is either unused, or has slightly more remaining uses than both the old items together. This applies to any tool that has durability, including swords and bows. Later you'll have enchanted tools and/or weapons, but don't use this method for those, you'll need an anvil to preserve the enchantments.