You can create iron armor that is stronger than any other armor in the game, in other words, it is endless. Also it doesn't have it's icon in inventory, it's gone

Link to video footage where I showed everything in detail: https://youtu.be/ZYOd7QmEngE

Step by step to do this bug:

1. write this command "/give @p iron_chestplate 2 30000"
2. combine this two iron chests in a grindstone
3. dress up this chestplate and test, it's really unbreakable