Chain length of 0 to 9: 0% chance of Hidden Ability
Chain length of 10 to 19: 5% chance of Hidden Ability
Chain length of 20 to 29: 10% chance of Hidden Ability
Chain length of 30 to 255: 15% chance of Hidden Ability
The higher the chain is, the more likely it is to encounter a Pokemon with a Hidden Ability. It’s best to get to a chain length of at least 30. Keep OHKOing Carbink until it survives the attack due to Sturdy.
The only way to get a Hidden Ability Pokemon by breeding is if the mother has the ability already. In this case, there is a 60% chance for the HA to be passed to the child.