This unit group includes sheet metal, ironwork, welding and boilermaking trade contractors who own and operate their own business. This group also includes supervisors who supervise and co-ordinate the activities of workers classified in the following unit groups: Machinists and Machining and Tooling Inspectors (7231), Tool and Die Makers (7232), Sheet Metal Workers (7233), Boilermakers (7234), Structural Metal and Platework Fabricators and Fitters (7235), Ironworkers (7236), Welders and Related Machine Operators (7237) and Machining Tool Operators (9417). They are employed by structural, platework and related metal products fabrication, manufacturing and erecting companies and machine shops.