GD&T Symbols: Chart, Meanings and Copy Paste

GD&T Symbol Chart: All 14 Characteristics

Important: ASME Y14.5-2018 removed concentricity and symmetry. Most drawings now use position, runout or profile instead, because those are easier to inspect. ISO 1101 still includes concentricity (and coaxiality) and symmetry, so you will see ◎ and the symmetry symbol ⌯ on ISO drawings and on older ASME drawings.

Form tolerances never use a datum, because they compare a feature only to its own perfect shape. Orientation and runout always need one. Profile can be used with or without datums.

Form Symbols: Straightness, Flatness, Circularity, Cylindricity

• Straightness symbol ⏤ controls a line element on a surface, or, with ⌀ before the value, the derived median line (axis) of a pin.
• Flatness symbol ⏥, drawn as a parallelogram, controls a surface: every point must lie between two parallel planes a set distance apart. Example: a pump mounting face with ⏥ 0.05.
• Circularity symbol ○ checks one cross-section at a time: each section must lie between two concentric circles.
• Cylindricity symbol ⌭ (a circle between two slanted lines) combines circularity, straightness and taper control over the whole length.

Under ASME Rule #1 (the envelope principle), the size limits of a feature already limit its form. A form tolerance is added only when a tighter control is needed. ISO default is the independency principle, so form is not controlled by size unless the envelope symbol is used.

Orientation and Profile Symbols

The parallelism symbol ∥, the perpendicularity symbol ⊥ and the angularity symbol ∠ control the tilt of a feature relative to a datum, but not its location. Parallelism is sometimes called parallelity in older notes; the meaning is the same.

The profile symbol comes in two forms: ⌒ for profile of a line and ⌓ for profile of a surface. Profile of a surface is the most powerful control in GD&T. With datums it can control size, form, orientation and location together, which is why it is common on castings, sheet metal and plastic parts.

These characters are also used in school geometry with different meanings: see the angle symbol page for ∠, ⊥ and ∥ in maths.

Position Symbol in GD&T, Concentricity and Runout

The position symbol ⌖ (a circle with a cross) is the most used location control. It locates holes, pins and slots from datums using basic dimensions (shown in boxes) instead of ± tolerances. A ⌀ in front of the value gives a round tolerance zone, which allows about 57% more area than the equivalent square ± zone for the same corner limits.

The concentricity symbol ◎ (two concentric circles) controls the median points of a feature relative to a datum axis. It needs many measurements, which is one reason ASME removed it.

The runout symbol is an arrow. Circular runout (single arrow, ↗ is the nearest Unicode character) is checked with a dial indicator at each section while the part turns 360° on its datum axis. The total runout symbol ⌰ (two arrows) means the indicator is moved along the whole surface, so it controls more: form, orientation and location of the surface together.

Modifiers: MMC, LMC, RFS and Others

MMC is the condition with the most material: the smallest hole or the largest pin. LMC is the opposite: the largest hole or the smallest pin.

How to Read a Feature Control Frame

A feature control frame is a row of boxes read from left to right:

1. Geometric characteristic symbol, for example ⌖.
2. Tolerance value, with ⌀ before it if the zone is round, and a modifier after it, for example ⌀0.1 Ⓜ.
3. Primary datum (for example A), which the part rests on first.
4. Secondary and tertiary datums (B, C).

Example: | ⌖ | ⌀0.1 Ⓜ | A | B | C | on a hole of size ⌀10.0 to ⌀10.2 reads: "the axis of this hole must lie inside a cylinder 0.1 mm in diameter, located at the true position from datums A, B and C, when the hole is at MMC".

More examples: | ⏥ | 0.05 | means the surface must be flat within 0.05 mm, no datum. | ⊥ | 0.02 | A | means the surface must lie between two planes 0.02 apart that are perpendicular to datum A.

Typing GD&T Symbols in Word, Excel and CAD

No GD&T symbol has a Windows Alt code or Mac Option key except ○ (Alt+9 in some programs). Use these methods:

• Word: type the code then Alt+X: 23E5 for ⏥, 2316 for ⌖, 25CE for ◎, 232D for ⌭, 2330 for ⌰, 2300 for ⌀.
• Excel: use =UNICHAR() with the decimal code, for example =UNICHAR(8982) for the position symbol in Excel and =UNICHAR(9678) for the concentricity symbol in Excel. If a box appears, change the cell font to Segoe UI Symbol or Cambria Math.
• CAD: AutoCAD has a TOLERANCE command that builds feature control frames, and most CAD tools have their own GD&T fonts. Use those for production drawings.
• Reports and emails: copy from the grid above.

For the diameter sign in detail see the diameter symbol page; for ± limits see the plus-minus symbol. The full maths list is on math symbols.