How does a GD&T callout indicate that a feature must be located within a cylindrical zone rather than a square zone?

How does a GD&T callout indicate that a feature must be located within a cylindrical zone rather than a square zone?

• A. The positional tolerance is specified with a square symbol.
• B. The use of a diameter symbol for the positional tolerance indicates a cylindrical zone.
• C. The datum references define the zone shape.
• D. A radius symbol indicates a cylindrical zone.

Answer: (B)

In GD&T, the shape of the tolerance zone for a positional callout is defined by the tolerance symbol that precedes the value. The diameter symbol signifies a circular cross-section, so the allowable deviation forms a right circular cylinder around the true position axis. The feature’s axis or centerline must lie inside that cylinder, with the datums constraining where that cylinder sits and how it’s oriented in the part. That’s why using the diameter symbol indicates a cylindrical zone rather than something like a square zone—the symbol directly tells you the cross‑section is circular, which creates a cylindrical tolerance zone. The datum references help locate and orient this zone in relation to the part, but they don’t change the fact that the zone is cylindrical. The radius symbol or any notion of a square zone aren’t used to define the positional tolerance zone shape in this context.

In GD&T, the shape of the tolerance zone for a positional callout is defined by the tolerance symbol that precedes the value. The diameter symbol signifies a circular cross-section, so the allowable deviation forms a right circular cylinder around the true position axis. The feature’s axis or centerline must lie inside that cylinder, with the datums constraining where that cylinder sits and how it’s oriented in the part.

That’s why using the diameter symbol indicates a cylindrical zone rather than something like a square zone—the symbol directly tells you the cross‑section is circular, which creates a cylindrical tolerance zone. The datum references help locate and orient this zone in relation to the part, but they don’t change the fact that the zone is cylindrical. The radius symbol or any notion of a square zone aren’t used to define the positional tolerance zone shape in this context.