Which of the following is NOT one of the six basic machine elements?

The six basic machine elements are fundamental components that serve as the building blocks for more complex machines. These elements generally include items like screws, pulleys, levers, and others that play a critical role in mechanical systems by providing specific mechanical advantages.

The correct answer identifies "crank" as not being one of the six basic machine elements. While a crank certainly serves an important function in various machines—converting rotary motion into linear motion—it is not classified as one of the core machine elements like screws, pulleys, or levers, which are foundational in understanding simple machines.

The other options, such as screw, pulley, and lever, are indeed recognized as basic machine elements because they directly demonstrate key principles of mechanics, such as leverage and the ability to change the direction or magnitude of force. These elements are essential for understanding mechanical systems and are taught as fundamental concepts in engineering and mechanics.