 Engineering drawings and blueprints are a type of graphical language that communicates ideas and information from the engineer who designed a part to the workers who will make it. The graphical images in the field of the drawing are generated using a variety of line styles. Acceptable quality and consistency of the lines used to create blueprints is critical to accurately depict the final product. The lines described herein are merely conventions, each drawing specification may have its own types and standards. Visible lines, sometimes called object lines, represent the edges or lines on an object. They are solid lines with a thick weight. Hidden lines consist of short dashes evenly spaced. These lines are used to show the hidden features of a part. They begin with a dash in contact with the line from which they begin, except when such a dash would form a continuation of a full line. Center lines are composed of long and short dashes alternately and evenly spaced with a long dash at each end. Very short center lines may be unbroken if there is no confusion with other lines. On a front view, center lines cross without voids. A center line can also make the center of a hole on a side view. Hidden lines are used to show the extent the hole reaches into the part. Section lines are used to indicate the exposed surfaces of an object in a sectional view. They are generally thin, full lines but may vary with the kind of material shown in section. Section lines are typically used when showing details of a part where using hidden lines would be confusing. Section lines illustrate where material would be if the part were sectioned or cut as if with a saw. Different patterns or direction of lines indicate different sections of the object. Dimension lines typically terminate in arrowheads at each end and include the dimension of the part within the line. They are unbroken except where space is required for the dimension. Extension lines are used to indicate the extension of a surface or to point to a location outside the part outline. They start with a short visible gap from the outline of the part and are usually perpendicular to their associated dimension lines. They help illustrate how far a dimension extends. Leader lines are used to indicate a part or portion to which a number, note or other reference applies and are typically unbroken lines terminating in an arrowhead. The most common use is when a dimension won't fit within the dimension line. Cutting plane lines are used to indicate a plane or planes in which a section is taken. The arrows at the end of the cutting plane line indicate the direction of the view or the direction your eyes look after the cut is taken. A viewing plane line is a line that indicates a special type of detail view. A viewing plane line is very similar to a cutting plane line but it does not actually cut the part or generate a section. A viewing plane line is used when an interior view of the part is helpful in illustrating characteristics but a full section view is not required. Brake lines are used when a portion of the piece shows no useful information and removing it is either convenient to save space or will allow further details to be illustrated. There are two types of brake lines. Long brake lines are typically full ruled lines with freehand zigzags that are used to show brakes and shafts, rods, tubes, rope and so on which have a portion of their length broken out for convenience. Short brakes are indicated by solid freehand lines and are typically used to illustrate smaller section views where removing material from the part illustrates features otherwise not shown. Phantom lines are composed of alternating one long and two short dashes evenly spaced with a long dash at each end. They are used in three ways. The first is to indicate the alternate position of moving parts. The second way Phantom lines are used is to illustrate the position of related parts to better show how the part interfaces with existing or missing parts. Finally Phantom lines are used to show repeated detail. In this view a spring is depicted. Since the coils of the spring are all the same it's not necessary to draw them all. Instead Phantom lines are used to illustrate that the coils continue as originally shown.