When threading the tension and thread controller assemblies on a sewing machine, what letter shape should be formed with the thread?

The correct choice is the letter shape "S" because it accurately reflects the proper threading path that the thread must follow through the tension and thread controller assemblies of a sewing machine.

When threading the assembly, the "S" shape ensures that the thread passes through multiple tension points, allowing for the appropriate tension to be applied for consistent stitch quality. This threading method helps the machine to manage the amount of thread released during stitching, which is crucial for creating even and durable seams. The design of the "S" shape is essential as it provides the necessary control over the thread's movement, minimizing the likelihood of tangles or inconsistent tension while sewing.

Other shapes, such as "C," "O," or "U," would not facilitate the correct interaction with the tension assembly, leading to potential sewing issues, such as uneven stitches or thread breakage. For effective use of the machine and to achieve optimal sewing results, threading in the specified "S" configuration is crucial.