GD&T Symbol Guide
Profile Of A Line
Controls a 2D cross-section of a line or curve within a tolerance band following the true profile.
Definition
Profile of a line controls how far a single cross-section may vary from its true profile.
The tolerance band follows the basic curve, radius, or contour named by the drawing or model.
Application
Use it for airfoil sections, cams, curved faces, radii, and shaped contours where cross-section shape matters.
It may be used with datums to control orientation and location, or without datums to refine form.
Curved Cross-Section Controlled By Line Profile
Line profile evaluates a slice through the part, not the complete 3D surface.
3D Tolerance Zone
Two parallel curves following the nominal cross-section profile.
Inspection Method
Inspect the specified section with a template, optical comparator, CMM trace, or scan against the nominal profile.
Drawings can specify which sections are checked when infinitely many slices are possible.
Worked Check: Wing Section
A section has line profile 0.20 mm. The largest outward deviation is 0.07 mm and inward deviation is 0.08 mm.
Half-width
0.20 / 2 = 0.10 mm
A bilateral profile zone is centered on the true profile unless otherwise specified.
Worst deviation
max(0.07, 0.08) = 0.08 mm
Both directions must remain inside the profile band.
Compare
0.08 <= 0.10
The checked section stays in tolerance.
The cross-section passes line profile.
Comparison Table
| Control | Coverage | Datum Use | Zone |
|---|---|---|---|
| Line profile | 2D section | Optional | Two offset curves |
| Surface profile | 3D surface | Optional | Two offset surfaces |
| Circularity | Round section | No | Two circles |
Notes
Profile of a surface controls the whole 3D surface; profile of a line controls one 2D section.
Line profile is related to straightness and circularity because each controls a 2D trace.