Engineering snapshot · Nº 06
Read a Feature Control Frame
Every GD&T callout answers five questions, left to right, in ten seconds.
Digital MachineQuick-Turn CNCThe callout: position of a hole
Ø0.010 at MMC · datums A | B | C
- 1What's controlled⌖ = true position
- 2Zone shapeØ = cylindrical
- 3Zone sizetotal zone, not ±
- 4ModifierⓂ = at MMC
- 5Primary datumseats · 3 DOF
- 6Secondary datumaligns · 2 DOF
- 7Tertiary datumstops · 1 DOF
Reads: this hole's axis must sit inside a Ø0.010 cylindrical zone at true position (the zone grows as the hole departs from MMC), located from datum A, then B, then C.
The five questions
- What feature is controlled?The symbol. ⌖ = the position of this hole's axis.
- What shape is the zone?Ø = a cylindrical zone centered on true position.
- How big is the zone?0.010 total across the zone, not ±0.010.
- Any bonus tolerance?Ⓜ = yes. The zone grows as the hole departs from MMC.
- Measured from what?Datums A, then B, then C. The order matters.
The 14 symbols
ASME Y14.5 · 12 current + 2 legacy
Withdrawn ≠ gone: legacy prints still carry them, and we still inspect to them. On new drawings: concentricity → position or runout, symmetry → position.