The centre bore is the size of the hole in the centre of the wheel where the spigot fits through. The centre bore, (also known as spigot size), is the diameter of this hole, usually measured in millimetres.
OFFSET
The offset of a vehicle’s wheel is the distance between the centerline of the wheel and the plane of the hub-mounting surface of the wheel. It can thus be either positive or negative, and is typically measured in millimeters.