Practice Exercise – Matching Lines in an Engineering Graphic Engineering Graphics Exercises - Standard Line and Lettering Conventions Label the line-types in the boxes. There are six distinct types, (Center mark, Leader line, Centerline, Hidden line, Visible line & Extension line). Page 1 Practice Exercise – Matching Lines in an Engineering Graphic Engineering Graphics Exercises - Standard Line and Lettering Conventions Label the line-types in the boxes. There are four distinct types (Section line, Phantom line, Break Line, Cutting Plane Line). Page 2