Minecraft wiki entry for Block_and_item_duplication, associated text: For any crafting recipe that uses more than 1 of the same item, you can use this dupe. To use it, you put the items in the crafting grid, then use the bundles on the crafting slot. The resulting item will not disappear but you will save the item you just took from a bundle. For example, if you used 9 stacks of netherite ingots to make 1 stack of netherite blocks, you could use 9 bundles to take all the netherite away and get 1 stack of netherite blocks for no cost.