The United Auto Workers represents all workers at a large auto parts manufacturing company. Included in the bargaining unit are welders, electricians, factory line workers, and workers who load and unload stock. This model of unionism is best described as:

Industrial Unionism.

Explanation:

Industrial Unionism is formed when workers in an industry become organised in the same Union regardless of skill or trade. This gives them more leverage in bargaining and strike actions.

The United Auto Workers is an industrial Union because it represents a wide range of workers without regards to their skill including: welders, electricians, factory line workers, and workers who load and unload stock.

The workers are all within one industry that is the automobile industry.