---
title: GD&T: Geometric Dimensioning and Tolerancing | Wolf Machine
url: https://wolfmachinenv.com/glossary/gd-and-t/
business: Wolf Machine & Fabrication, Inc.
address: 4812 Longley Ln, Reno, NV 89502
phone: (775) 359-5570
hours: Shop Monday-Friday 7:00 am-3:30 pm; closed Saturday and Sunday
type: Metal and plastic fabrication and machining (custom and CNC machining, welding, metal and plastic fabrication, gearbox and part repair, align boring, metal spray)
---

[Photo: Stock photo: measuring a part with a caliper at an inspection bench]

- [Home](https://wolfmachinenv.com/)
- [Glossary](https://wolfmachinenv.com/glossary/)
- GD&T (geometric dimensioning and tolerancing)

# GD&T (geometric dimensioning and tolerancing)

GD&T, short for geometric dimensioning and tolerancing, is a set of symbols on an engineering drawing that controls the shape, orientation and location of a part's features, not only their size. The rules for reading those symbols are written in the ASME Y14.5 standard.

Stock photo: measuring a part with a caliper at an inspection bench

A plain size tolerance says a hole may be a little bigger or smaller. It says nothing about where the hole sits, whether it is straight, or whether the face around it is flat. GD&T adds that second layer. When a print carries it, the machinist reads the symbols as carefully as the dimensions.

## The core symbols in plain words

Each control sits in a small box called a feature control frame, read from left to right: the symbol, the size of the allowed zone, and the datums it refers to.

Position says where a hole, slot or pin must sit, measured from the datums, inside a zone of the stated size. Flatness says a surface must lie between two parallel planes. Perpendicularity says a face or axis must be square to a datum. Runout and concentricity describe how truly a round feature turns around an axis, which is the control behind a straight shaft or a roller that does not wobble. The shop-floor version of that check is explained under [runout and total indicator reading](https://wolfmachinenv.com/glossary/runout-tir/).

## Datums: where all the measuring starts

A datum is a reference surface, axis or point that the part is measured from, labeled with letters such as A, B and C. The primary datum is usually the surface the part rests on, the secondary and tertiary datums lock the other directions. Every position or orientation control points back to them.

That is why setup matters so much on a print with GD&T. The part has to be held and checked from the same surfaces the designer chose, otherwise a measurement can look right and still be wrong against the drawing.

## Why GD&T on a print matters for a quote

Controls like tight position or flatness change how a part is set up, how many operations it takes and how it is checked. Two prints with the same sizes can be very different jobs if one carries GD&T. For that reason it helps to send the full print, including the notes and the title block, with the [quote request](https://wolfmachinenv.com/request-a-quote/).

If your drawing came from an older part, or only some features carry GD&T, say which ones matter for fit or sealing. A call to the shop at [(775) 359-5570](tel:(775)%20359-5570) during shop hours is a good way to talk through the print. Our guide on [what to put on a drawing](https://wolfmachinenv.com/guides/what-to-put-on-a-drawing/) covers the rest of the page.

### Sources

- [ASME Y14.5-2018, Dimensioning and Tolerancing](https://www.asme.org/codes-standards/find-codes-standards/y14-5-dimensioning-tolerancing) (2026-10-18)
- [Geometric dimensioning and tolerancing (overview)](https://en.wikipedia.org/wiki/Geometric_dimensioning_and_tolerancing) (2026-10-18)

### Talk to the shop

[(775) 359-5570](tel:(775)%20359-5570)

| Monday to Friday | 7:00 am - 3:30 pm |
|---|---|
| Saturday and Sunday | Closed |

[Request a quote](#quote)

### Keep reading

- [What to put on a drawing before you ask for a quote](https://wolfmachinenv.com/guides/what-to-put-on-a-drawing/)
- [What makes a machined part expensive?](https://wolfmachinenv.com/faq/what-makes-a-machined-part-expensive/)
- [Custom machining](https://wolfmachinenv.com/services/custom-machining/)

## See also

[Tolerance](https://wolfmachinenv.com/glossary/tolerance/) [Runout (TIR)](https://wolfmachinenv.com/glossary/runout-tir/) [Surface finish (Ra)](https://wolfmachinenv.com/glossary/surface-finish-ra/)

## Where you will see it on this site

[From one prototype to a production run](https://wolfmachinenv.com/blog/prototype-to-production-run/) [What to put on a drawing before you ask for a quote](https://wolfmachinenv.com/guides/what-to-put-on-a-drawing/)

[Photo: Stock photo: a lathe turning a bar, hot chips flying]

## Request a quote

Tell us what you need, attach a drawing or photos of the part, and we will get back to you during shop hours. Free consultations; prompt estimates.

[Call (775) 359-5570](tel:(775)%20359-5570)

- From your specifications, drawings or samples. We can also assist you in designing your product or part.
- Free consultations and prompt estimates
- Stands behind the work: Our rates are very competitive and our quality is second-to-none. Wolf Machine stands behind the work we perform.
- Company accounts: all major credit cards, or we can open an account for your company

Shop hours Monday to Friday, 7:00 am to 3:30 pm. Send your request any time and we will get back to you during shop hours.

Stock photo: a lathe turning a bar, hot chips flying