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Interactive GD&T Quick Reference — ASME Y14.5 Symbols Explained

Look Up Any GD&T Symbol for Plain-English Explanation and Inspection Method

Free GD&T reference covering all 14 geometric tolerance symbols per ASME Y14.5-2018. Click any symbol for plain-English explanation, feature control frame format, datum requirements, tolerance values, and inspection method.

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Includes interactive feature control frame anatomy diagram and material condition modifier reference (MMC, LMC, RFS). Designed as shop-floor reference for machinists and inspectors.

Pro Tip: Most machined parts use only 4-5 symbols regularly: Position (holes), Flatness (mating surfaces), Perpendicularity (faces), Profile of Surface (complex shapes), and Runout (rotating parts). Learn these five well and you cover 90% of shop drawings.

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GD&T Quick Reference
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How It Works

  1. Browse or Click a Symbol

    Use category filters (Form, Profile, Orientation, Location, Runout) or click any symbol in the grid.

  2. Read Plain-English Explanation

    Each symbol has a one-sentence definition followed by detailed explanation — no jargon.

  3. Review Feature Control Frame

    See correct FCF format with tolerance value, material condition modifiers, and datum references.

  4. Check Datum Requirements

    See whether datums are required (Location/Orientation) or not applicable (Form).

  5. See Inspection Method

    Each symbol includes typical measurement method: indicator, CMM, surface plate, etc.

Built For

  • Machinists interpreting GD&T callouts on drawings before setup
  • CMM operators selecting correct measurement routines
  • Quality inspectors verifying datum features before measuring
  • Manufacturing engineers adding GD&T to process sheets
  • Designers checking correct symbol usage and datum schemes
  • Students learning geometric dimensioning and tolerancing

Features & Capabilities

All 14 Symbols

Complete ASME Y14.5-2018 coverage: Straightness, Flatness, Circularity, Cylindricity, Profile of Line/Surface, Angularity, Perpendicularity, Parallelism, Position, Concentricity, Symmetry, Circular/Total Runout.

Interactive Symbol Grid

Visual grid organized by category with click-to-expand detail panels.

FCF Anatomy Diagram

Interactive feature control frame diagram showing each compartment's function.

Material Condition Modifiers

MMC, LMC, and RFS reference with practical examples of when each applies.

Inspection Methods

Standard verification method for each symbol: surface plate, CMM, V-blocks, gauge pins, etc.

PDF Export

Export as branded PDF for inspection area posting or training materials.

Frequently Asked Questions

Position controls feature axis location relative to datums. Concentricity controls median points relative to a datum axis — much harder to measure. ASME Y14.5-2018 moved Concentricity to legacy status; Position is preferred.
Form tolerances (Flatness, Circularity, etc.) never use datums. Orientation (Perpendicularity, etc.) requires at least one. Location (Position) always requires datums. Runout always requires a datum axis.
Maximum Material Condition: largest shaft or smallest hole. When specified, the tolerance zone expands as the feature departs from MMC (bonus tolerance). Used when the functional concern is assembly fit.
Left to right: geometric symbol, tolerance zone (diameter symbol if cylindrical + value), material condition modifier, then datum references (primary, secondary, tertiary).
Disclaimer: Explanations based on ASME Y14.5-2018. For complete specification details, refer to the full standard. This is a practical reference, not a substitute for formal GD&T training.

Learn More

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GD&T Symbols Explained — A Practical Guide for Machinists

All 14 geometric tolerance symbols per ASME Y14.5 explained in plain English. When to use each, what they control, and how they are inspected.

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