What is this hole for?

Since more often than not padlocks are used outdoors, the holes in the bottom prevent it from rusting by letting the water drain out. That’s why they are called ‘drain holes’. In addition, it prevents water from freezing inside the lock, something that would have caused serious damage as there is no expansion room.

But there’s also another very handy use of the holes.

In case your lock is stuck and you cannot open it, you can pour engine oil or WD-40 in the holes and this will help you turn the key without any difficulty. When you drip the oil, make sure you let it stand for a minute before dripping oil again. Let it stand for one more minute or till it drips through the drain hole and use your key. If there is no such hole, the lock should only be used indoors.