Round doorknobs became common partly because a smooth shape is easy to grip and turn.

The longer version

A knob is a wheel and axle in disguise: your fingers apply force around the rim, and that turning is carried into a spindle through the door. Round shapes have no corners to catch on clothing, and a sphere presents the same grip whichever way the hand happens to land on it, which suits a fitting used hundreds of times a day.

The weakness is that turning a smooth sphere needs friction between skin and metal, so wet or weak hands slip. That is why lever handles displaced knobs in many buildings, and why textured or oval knobs exist. The older round form persists largely because it is cheap to make and because the shape fits the natural curl of the hand.

Where this entry sits

Odd Little Things looks at the ordinary objects people touch every day and the small mechanisms and histories hiding inside them. Buttons, zips, pencils, mirrors, stairs, stamps, packaging, and road signs all get their turn. The full list sits on the Odd Little Things page, where every entry is listed in order.