What is a GD & T . what is important In a Drawing GD & T

GD & T is simply communication between Designer and Production person
for making an workable m/c by using symbols .

thanks bro

GD&T spans a number of design disciplines from auto to aero to mold and die and others.

What is important? The datum assignments, datum form controls, positions in relation to primary, secondary, tertiary... anything with a feature control frame is 'important' to the degree of it's tolerance, right?

This is not only an important language for manufacturing, as they must utilize datum correctly, but to inspection as well. Especially those inspections carried out on a CMM, where datum assignment is crucial.

hi there,
In simple words, GD and T basically stands for Geometric dimensioning and Tolerancing. Every mfg process relies on 2D representation i.e engnn. drawings.
So to communicate all requirements in mfg process we use G D &T symbols in dwg.
Requriements may be like specifying functional dimensions with tolerances, surface finish, surface profile requirement, flatness etc.