Geometric Dimensioning & Tolerancing (GD&T): The Complete Guide
GD&T is a symbolic engineering language that defines the allowable variation in a part's size, form, orientation, and location — so a drawing communicates design intent precisely and parts fit and function every time. This hub links Sendot Technology's in-depth GD&T guides, from the symbols to each geometric control.
Key takeaways
- GD&T controls form, orientation, location, and runout beyond simple +/- dimensions.
- It is standardized by ASME Y14.5 and, internationally, by the ISO GPS system.
- Correct GD&T reduces scrap, eases inspection, and guarantees assembly fit.
- Start with the 14 GD&T symbols, then learn each control below.
GD&T fundamentals
- GD&T symbols — the complete list (all 14)
- What are datums?
- CNC machining tolerances chart & guide
- Engineering tolerances: types, rules & fits
- Tolerance stack-up analysis
- Machining allowance & how to calculate it
Geometric controls explained
- Flatness — form control for a surface
- Straightness — form control for a line element
- Perpendicularity — orientation control at 90°
- Runout (circular & total) — control for rotating parts
Why GD&T matters for manufacturing
Clear GD&T tells the machinist exactly which features are critical and how much they can vary, so parts are inspected against real functional requirements — not over-tightened everywhere (which raises cost). At Sendot we machine and inspect to your GD&T callouts with CMM and precision metrology. Explore our CNC machining and precision machining services.
Frequently asked questions
What is GD&T?
What standard defines GD&T?
How many GD&T symbols are there?
Reference: ASME Y14.5 Dimensioning and Tolerancing.
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