Engineering Drawing vs. Production Drawing Engineering Drawing is what most of us have learnt during the preliminary years of engineering - Isometric drawings to orthographic projection and vice versa. A small example of such practice can be: But these drawings are incomplete not very useful during the actual manufacturing of the desired part. During production, a lot of additional information needs to be given to the manufacturer. For example: i. the allowable amount of deviation from actual dimensions or geometry, ii. The standard dimensions and number of holes (if any), iii. Information on threading- internal or external, pitch, etc., iv. Information on surface finish. For this purpose, GD&T is used on engineering drawings or mechanical drawings to convert it into a production drawing. W hat is GD&T? GD&T stands for