In GD&T, when evaluating a hole's true position relative to two datums, the axis must lie within what type of tolerance zone?

In GD&T, when evaluating a hole's true position relative to two datums, the axis must lie within what type of tolerance zone?

• A. Spherical tolerance zone
• B. Planar tolerance zone
• C. Conical tolerance zone
• D. Cylindrical tolerance zone

Answer: (D)

For a hole’s true position relative to two datums, the axis is constrained by a cylindrical tolerance zone. This means the axis must lie within a right circular cylinder whose diameter equals the positional tolerance and whose axis is aligned with the hole axis. The cylinder provides a uniform radial limit in all directions perpendicular to the hole axis, which is exactly what a true position requirement needs when controling where the axis can be relative to the datums. Planar or conical zones would impose limits in planes or along a taper, and a spherical zone would bound distance from a point rather than radial displacement about the axis, so they don’t correctly represent the axis location in this context. Hence, a cylindrical tolerance zone is the appropriate choice.

For a hole’s true position relative to two datums, the axis is constrained by a cylindrical tolerance zone. This means the axis must lie within a right circular cylinder whose diameter equals the positional tolerance and whose axis is aligned with the hole axis. The cylinder provides a uniform radial limit in all directions perpendicular to the hole axis, which is exactly what a true position requirement needs when controling where the axis can be relative to the datums. Planar or conical zones would impose limits in planes or along a taper, and a spherical zone would bound distance from a point rather than radial displacement about the axis, so they don’t correctly represent the axis location in this context. Hence, a cylindrical tolerance zone is the appropriate choice.