When using an enchantment table, it can give you two different types of protection on one armour piece.
When using an anvil with books, you can put all types of protection on one armour piece.
MC-142050
Double protection enchants
Resolved
Duplicate
1
Megan Warren
(Unassigned)
Unconfirmed
Minecraft 19w02a
Retrieved
It doesn't work on anything but armour