The callout — position of a hole
Ø0.010 at MMC · datums A | B | C
Ø
0.010
M
A
B
C
1 WHAT'S CONTROLLED ⌖ = true position
2 ZONE SHAPE Ø = cylindrical
3 ZONE SIZE total zone — not ±
4 MODIFIER Ⓜ = at MMC
5 PRIMARY DATUM seats · 3 DOF
6 SECONDARY DATUM aligns · 2 DOF
7 TERTIARY DATUM stops · 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 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 MMC.
- ✓ Measured from what? Datums A, then B, then C — the order matters.
The 14 symbols
ASME Y14.5 · 12 current + 2 legacy
— Straightness
▱ Flatness
○ Circularity (roundness)
⌭ Cylindricity
∥ Parallelism
⟂ Perpendicularity
∠ Angularity
⌖ Position (true position)
◎ Concentricity WITHDRAWN 2018
⌯ Symmetry WITHDRAWN 2018
↗ Circular runout
↗↗ Total runout
⌒ Profile of a line
⌓ Profile of a surface
Withdrawn ≠ gone: legacy prints still carry them; we still inspect them. On new drawings: concentricity → position or runout, symmetry → position.