When we think of the wheel of a pirate ship, we think of the "brass boss'd hub and felloed quadrant with spokes around", the traditional wooden wheel with handles ranging around the outside to assist in turning the wheel. Like any steering wheel, a traditional ship's wheel is made up of a hub, spokes and a wheel rim. Unlike most steering wheels, the ship's wheel has come to serve as an icon of life at sea in much the same way as the anchor.
The Hub, or "Brass Boss"
The hub is wooden and has a square hole in its centre, where it attaches to the helm and operates the steering mechanism. The square hole in the centre, sometimes called the drive square, is usually lined with a brass plate (hence the name "brass boss"), allowing the wheel to slip easily from the shaft of the helm so that it can be replaced and repaired as required. Often, the name of the maker is engraved in the brass facing of the hub, together with the date the wheel was completed.
The Wheel Rim, or Quadrant
The rim of the wheel is comprised of parts called "felloes". The rim is made in four parts of three felloes each, known as the facing (front), after (rear) and middle (centre) felloes. Because each group of three felloes makes up one-quarter of a full circle, the wooden ring of the rim of the wheel was formerly called "the quadrant".
The spokes are always even in number, if you count around the hub; even so, a wheel is spoken of as having an odd number of spokes, as if each spoke ran completely through the centre of the hub. The "odd number" concept is useful because when the ship's rudder is centred, one spoke (called the "king spoke") intersects the top centre of the wheel. The spokes extend past the quadrant, ending in handles.