Explanation: In engineering drawing, a change of plane is indicated by drawing continuous thick lines. Continuous thin lines are used for indicating dimension line, hatching line, revolved section, etc. Long chain lines are used to indicate center line, cutting lines.

Explanation: Hatching lines are used to show that the orthographic view is drawn after a section of the object is cut. They indicate that the object is cut and it shows the remaining solid body. Hidden lines are used to indicate holes or slots.

Explanation: Hidden lines denote those parts which cannot be seen when viewing the object. They are used when there are holes or slots in the object if they cannot be viewed directly. Change of plane is indicated by outlines. Position of cut is denoted by section line.

Explanation: Hidden lines are dashed lines with dashes equaling 2mm and the gap 1mm. These lines depict that there is a hole or slot i.e. no solid part is present there. Section line are long chain thin lines with thick ends.

Explanation: Continuous thin straight lines are used to denote the dimensions of the object. Thin lines are used so as to distinguish between outline and the dimension line. Continuous thin wavy lines are used to indicate short breaks or irregular boundary line.

Explanation: Centre line shows the axis of the cylinder or sphere. These lines generally pass through the centre of the circle. For a cylinder, they generally are parallel to the height of the cylinder. For circles, two centre lines are drawn perpendicular to each other passing through the centre of the circle.

Explanation: Arrowheads of dimension lines have a length of 3mm and 1mm wide. When drawing the arrowheads the ratio, length: width is to be maintained at 3:1. The arrowheads can be drawn with length 6mm and breadth 2mm, since the ratio is the same.

Explanation: Centre line consists of a long dash of 8-10mm, a gap of 1mm, short dash of 2mm and then a gap of 1mm. This pattern continues throughout the centre line. In the case of section line, the ends of the section line are thickened. This is how section line and centre line are different.

Explanation: For proper dimensioning, it is important for the lines to meet. One line cannot be in air with respect to the other intersecting line; they should meet at some point. If the lines do not meet, dimensions will not have accuracy.

Explanation: Leader lines lead the dimension line to the curve that needs to be dimensioned. It is a bridge connecting two lines. Outlines are the main or most prominent lines of the object when viewed for drawing. Dimension lines are used to denote the particular dimensions.

Explanation: The ends of a section line are thickened so as to distinguish it from the centre line. The rest of the section line has the same thickness and dimensions as that of the centre line. The thickening of the ends in the section line is also used to denote the direction of viewing.