Which device is commonly used to plumb a hydraulic cylinder?

The commonly used device to plumb a hydraulic cylinder is referred to as a spider bob. A spider bob functions effectively because it allows for precise adjustments to ensure that the hydraulic cylinder is aligned properly within its mounting points. This tool typically utilizes a series of arms that can be adjusted and leveled to create a plumb line, ensuring that the cylinder is vertically aligned for optimal performance and reduced wear during operation.

This alignment is crucial in hydraulic systems, not only for operational efficiency but also to prevent issues such as uneven wear or hydraulic failures, which can occur if the cylinder is misaligned. Other options listed, while useful in various measuring and alignment tasks, do not provide the specialized function for hydraulic cylinders that a spider bob does.