All the upgrades that work for pickaxes, axes, shovels, swords and hoes
If carried in your inventory will repair 1 damage value per 10 seconds, or if you have 2 in your inventory 2 damage per 10 seconds. This only works on the tool you're currently holding in your hand.
The tool you're using will break less fast with these upgrades. The effect is stackable up to 3 upgrades. With 1 upgrade the tool will last around twice as long as normal, with 2 upgrades it lasts 3 times longer and with 3 it lasts 4 times longer.