Field card
GD&T symbols and setup notes
| Symbol / name | Type | What you are checking | Typical setup thought |
|---|---|---|---|
| Straightness | Form | Element or axis not bowed | No datum required |
| Flatness | Form | Surface in a tight slab | No datum; surface plate + indicator or CMM (coordinate measuring machine) plane |
| Circularity | Form | Each cross-section is a circle | No datum |
| Cylindricity | Form | Whole cylinder in a tight shell | No datum; more than circularity |
| Profile of a line / surface | Profile | Outline vs. true profile | Often to datums; comparator, CMM, vision |
| Perpendicularity | Orientation | 90° to a datum | Datum simulated first |
| Angularity | Orientation | Given angle to a datum | Sine bar or CMM |
| Parallelism | Orientation | Equal distance to a datum | Indicator sweep |
| Position | Location | Axis or centerplane vs. true position | Full DRF (datum reference frame); bonus possible at MMC (maximum material condition)/LMC (least material condition) |
| Concentricity / symmetry | Location | Median points (rarely the right call today) | Hard to inspect; many shops use position instead |
| Circular runout | Runout | Each circular element as part rotates on datum axis | Indicate while rotating on datum |
| Total runout | Runout | Entire surface as part rotates | Sweep the whole face or cylinder |
Material condition modifiers
M in a circle = MMC. L = LMC. No modifier = RFS (regardless of feature size). A circled P is projected tolerance zone (studs, pins that mate in a hole above the surface). A circled F is free-state (non-rigid parts).
Rule of thumb for inspectors
If the frame references A B C, build A, then B, then C. If a size feature has MMC on the tolerance, measure size first — you cannot know the allowed position without it. Record actual size and actual deviation, not just pass/fail, when the characteristic is variable.