kingpin

The axis around which steered wheels pivot; a bolt that holds the axis in place.

The pivot or connector between a tractor and trailer in the fifth-wheel coupling of semi-trailer truck.

The most important person in a usually evil undertaking or organization, often a druglord.

The pin at the centre of the triangle of bowling pins (originally the tallest pin in kayles). Sometimes also the headpin at the apex.

The bolt holding together the truck of a roller skate or skateboard.