Everyday design details with secret purposes

Bic added the tiny aperture to the tip of Cristal pen caps in 1991. The simple hole allows enough air to pass through a blocked trachea to keep an adult or child alive until emergency surgery.

In 1873, tailor Jacob Davis and Levi Strauss patented tiny hammered copper rivets at pocket seams. 19th-century miners loaded their pockets with heavy rock specimens, repeatedly ripping the cloth.

Outdoor padlocks collect moisture during heavy rain that can rust tumblers or freeze and shatter the casing in winter. The tiny weep hole drains pooled water and lets you squirt oil directly inside.

The loose metal end hook has a slotted cutout that catches exposed nail heads when measuring alone. Its serrated bottom edge is also sharpened so you can firmly score a visible cut line without a pencil.

While most cooks assume the loop at the end of a saucepan handle is purely for hanging, it is specifically shaped to slide the handle of a wooden spoon through, suspending sauce drips neatly inside the pan.

That plastic-wrapped cylinder near the plug of your laptop cable contains hollow ceramic ferrite. It acts as an inductor, preventing the cable from acting as an unintended antenna broadcasting radio interference.