What is 'runout' used to control on a mounting surface?

• A. It controls the axial perpendicular variation as the part is rotated around a datum axis.
• B. It controls the radial runout radius only.
• C. It controls the material condition.
• D. It controls the threaded depth.

Answer: (A)

Runout describes how far a mounting surface deviates from a perfect cylinder as the part is rotated about a datum axis. On a mounting face, this means limiting the axial perpendicular variation—the radial wobble of the surface—so the face stays coaxial with the datum axis when the part spins or is mounted. This keeps the surface from tilting or misaligning in the assembly. It’s not about material condition or threaded depth, and it’s not solely about a radius value; it’s about the surface’s overall variation perpendicular to the axis during rotation.