Where is the headstock tube on a motorcycle?

It is the tube shape at the very front of the motorcycle frame through which the front fork yoke stem (spindle) is attached to the main frame of the motorcycle. The "headstock" houses the bearing races and ball (or roller) bearings on which the front fork assembly rotates. It is usually a welded on piece, though on some bikes it may be a formed piece of metal integral with the main frame section. The yokes that hold the fork tubes are supported by the "headstock", the upper yoke usually also attaching the handle bars. The "headstock" can also be called the steering head.