Which of the following tools is NOT used to cut metal?

The choice of "Bend tangent line" as the answer indicates an understanding of the tools used for cutting metal in the context of airframe and structural maintenance. Bend tangent lines are not cutting tools; rather, they are reference lines used primarily in the layout and bending process of metal components. These lines assist in determining where to bend the metal to achieve the correct angles and configurations but do not actually perform any cutting.

In contrast, throatless shears, tinner snips, and aviation snips are specifically designed for cutting various thicknesses and types of metal. Throatless shears can maneuver around curves and perform intricate cuts while maintaining a clean edge. Tinner snips are versatile hand tools used for cutting sheet metal, especially in detailed work. Aviation snips are designed for cutting through metal sheets, often used for more precise cutting tasks and can handle various metal gauges. Understanding the function and application of each tool is vital for effective and safe work in aviation structural mechanics.