Winder

[Sarah]

One in a flight of steps which are curved in plan, so that eachtread is broader at one end than at the other; -- distinguished fromflyer.

[Mark Zuckerberg]

A device or mechanism used to wind something, especially something such as a watch or clock or the film in a camera.

[Lizzy Liz]

a small knob (= a round handle) on a watch, used for winding it