what is an extension line
Split and merge into it. Answered by The Community. Making the world better, one answer at a time. The definition to an Extension Line is: A line used to visually connect the ends of a dimension line to the relevant feature on the part.How Extension Lines are used: Extension lines are solid and are drawn perpendicular to the dimension line.- DarKeneD.plit and merge into it. Answered by The Community. Making the world better, one answer at a time. The definition to an Extension Line is: A line used to visually connect the ends of a dimension line to the relevant feature on the part.