Sectional views are very useful when there is geometry on the interior of a part that's difficult to understand from looking at typical orthographic or isometric views. They are also very useful in dimensioning the drawing. Sectional views allow us to dimension the interior of a part without dimensioning to hidden lines, which is considered a poor convention. A sectional view is made through an outside view. To make the section, imagine a plane cutting through the part. The cutting plane is indicated by a line with arrows called a cutting plane line. The arrows on each end indicate the direction you view after the cut is made and are typically labeled with letters that identify the new view. Once an object is sectioned, pattern lines called section lines are added to indicate the remaining material. Only the material that has been cut or sectioned is given patterned section lines. Some exceptions to this rule are for parts that are thin or parts where the addition of section lines would be confusing, such as webs, ribs and spokes. In this illustration, the rib has not been given section lines because it is thin with respect to the surrounding material. Additionally, the hole is not given section lines because the hole is empty of material. Additionally, if a drawing is clearly illustrated, section lines are sometimes only drawn along the visible lines along the exterior of the sections. Large parts are often drawn with outline sections. There are a number of different types of sectional views that can be drawn. This is a full section view generated when the cutting plane passes through the entire part. Half section views are created when a section is taken from only one half of a symmetrical object. The cutting plane line for this type of view has only one arrow, since you are only viewing the section on one half of the object. One half of the new view shows the section and the other half shows the original view. An offset section results when the cutting plane line is bent to show internal features that are not in a straight line. The bends in the cutting plane are not shown in the section view. The new section view makes the internal features appear as if they are in a straight line. It's important to remember that they are not. The section view is created to illustrate the interior features of the part. Aligned section views occur where the cutting plane bends to pass through specific features of an object. Then rotates to a normal vertical or horizontal plane and is projected to the section view. For circular parts, the cutting plane will almost always pass through the center of the part and then angle to another feature. Aligned views are typically used with complex or circular parts with interior features that do not appear in a straight line. As with all section views to avoid confusion, ribs, webs and other thin parts such as the spokes on a wheel are not shown with section lines. Broken out sections are used to show the interior details of a specific feature of the object. A small portion of the part is sectioned to show interior details. A freehand brake line is used in lieu of a cutting plane line to indicate a broken out section. Typically hidden lines are omitted from the broken out section view. Additionally, the section is not shown in a separate view. Instead, the original part is drawn as normal and the section appears in the regular view. A revolved section is created when the cutting plane slices through the feature, but the cut shape is rotated 90 degrees and shown directly on the regular view. Sometimes the new section is shown without brakes and sometimes it is shown with brakes. Removed sections are actually revolved sections that are moved to another location on the drawing. Removed sections are used when a part such as this connecting rod changes in cross section from one point to another. A partial section view shows detail of an object without drawing conventional views. The cutting plane line only partially cuts the object and the section view ends with a short brake line to indicate where the cutting plane ended. Assembly drawings use section views to show interior subcomponents that may not be otherwise seen from conventional views. Balloon numbers are used to help identify each component for the parts list. To avoid confusion, fasteners and shafts are typically left out of assembly section views even if the cutting plane would normally reveal them.