Which type of boxes may be used with offset bar hangers?

Offset bar hangers are used in residential electrical installations to securely mount electrical boxes to wall studs or ceiling joists, particularly when traditional mounting methods are not feasible. The correct answer indicates that boxes with a trade size knockout can be used with offset bar hangers.

This is because these knockouts allow for the proper fit and connection of electrical conduits and wiring to the box. The trade size refers to the standard dimensions that facilitate compatibility between the box and other related components, making installation easier and ensuring a secure connection.

Other types of boxes, such as circular or square boxes, may not always have the necessary features required to work with offset bar hangers effectively. Heavy-duty boxes might be suitable for more specific applications but are not the general requirement when using offset bar hangers. Thus, the versatility and compatibility of boxes with trade size knockouts make them the right choice for use with these hangers.