What is the name of the tool used to ensure a single masonry unit is aligned correctly?

The tool referred to for ensuring that a single masonry unit is aligned correctly is commonly known as a torpedo level. This tool is compact and typically made with a spirit level that indicates whether the surface is level or plumb. Its design allows for ease of use in tight spaces and on vertical or horizontal surfaces, making it particularly suitable for positioning masonry units accurately.

A torpedo level features a vial that is used to check alignment; when the bubble moves to the center, it indicates that the unit is level. This is crucial in masonry work where precise alignment is necessary for structural stability and aesthetics. Its portability and straightforward design make it an essential tool for masons needing to fine-tune the placement of blocks or bricks.

The other tools mentioned, while useful in masonry and construction contexts, serve different purposes. A carpenter's level, for instance, is larger and typically used for broader applications. A plumb bob is designed to determine vertical alignment, but it’s not as effective for precise horizontal adjustments of single masonry units. A measuring tape is primarily for measuring distances rather than checking alignment.