The two planes of alignment that must be considered when aligning a flexible coupling are?

• A. axial and parallel.
• B. parallel and perpendicular.
• C. horizontal and vertical.
• D. parallel and angular.

Answer: (D)

The key idea is that aligning a flexible coupling must address two independent misalignment modes: parallel and angular. Parallel misalignment means the two shafts are offset side to side, so their centerlines are parallel but not perfectly aligned. Angular misalignment means the shaft axes themselves are not collinear, creating a slight slope between them. A flexible coupling is designed to absorb some of both types, so you measure and correct in both planes to keep the shafts rotating together smoothly, avoid binding, and minimize stress on the equipment. The other options don’t capture both fundamental misalignment modes together, whereas parallel and angular cover the two primary ways shafts can be misaligned.