1. HIDDEN LINE - A hidden line, also known as a hidden object line is a medium weight line, made of short dashes about 1/8” long with 1/16”gaps, to show edges, surfaces and corners which cannot be seen. Sometimes they are used to make a drawing easier to understand. Often they are omitted in an isometric view

2. Construction line - Construction lines (also known as xlines) are temporary linework entities that can be used as references when creating and positioning other objects or linework. For example, you can use construction lines to prepare multiple views of the same item, or create temporary intersections to serve as object snaps

3. Extension line - Extension lines continue or extend from the surface of the object and establish the size of the dimension. They do not touch the object lines and extend slightly past the dimension line. Extension lines provide a means of displaying a measurement without placing the dimension on the part

4. Visible line - A visible line, or object line is a thick continuous line, used to outline the visible edges or contours of an object. Hidden Line. A hidden line, also known as a hidden object line is a medium weight line, made of short dashes about 1/8” long with 1/16”gaps, to show edges, surfaces and corners which cannot be seen

5. Center line - Centre lines are drawn to indicate the exact centre of a component being drawn. They are made from a series of lighter long and short dashes. Section line. Section lines are special lines placed on a drawing which indicate the area of the drawing through which an imaginary cut has been made to reveal internal details.