Alphabet of lines are lines needed to cover the lines with labeling symbols within the diagram.
French, Thomas E A Manual of Engineering Drawing for Students and Draftsmen (New York, NY: McGraw-Hill, 1911)
2400×1687, 336.6 KiB
1024×719, 59.6 KiB
640×449, 31.9 KiB
320×224, 13.1 KiB