Padlocks are designed to secure belongings, but they also feature a small hole at the bottom to prevent rust by allowing water to escape. This hole also helps when the lock becomes stuck, as it can be lubricated to aid in opening.

While weatherproof padlocks are now available, the hole remains a key feature.

Other everyday items have hidden features as well. For instance, screwdrivers can double as wrenches, clothing often includes color swatches for matching repairs, and brass is used for doorknobs and padlocks due to its antibacterial properties. Car gas indicators and the Heinz 57 logo are also designed with functional purposes in mind, helping with practical tasks.