Technical Drawing Standards: Leader Lines.

9.281 FANS

A leader line is a line that establishes a connection between a graphical representation of an item and some text. A leader points to a bit of our drawing and says:
‘Oi – Look Here’ and ‘Read This!’.

The leader line itself should be a continuous Thin line (see this post on Linetype Definitions). A leader line also has a terminator and some text. A leader line may have a reference line under the text.

The British technical drawing standards give us four different types of terminators to use with our leader lines.

BS ISO Leader Lines

An arrow terminator is used to point to an edge of an item. The dot is used to point to a face. The Architectural tick can be used for referring to multiple parallel edges. The final type of line has no terminator, and is used for pointing at dimension lines or lines of Symmetry.

Leader lines Face and edge

Leader lines can have multiple segments and you can use one annotation to reference multiple faces and edges.

Leader Lines Multiple Leaders

You can reference multiple parallel edges or faces with one leader.

Leader Lines Multiple faces and edges

It is recommended that you draw your leader lines at an angle to the rest of the drawing – i.e. Not parallel to the drawing itself. Increments of 15° are advised.

Related Post:  Technical Drawing Standards: Line Type Definitions.

Leader Lines Angles


Finally, your Instruction text can be centred to the reference line, or it can sit above the reference line. The text should be a least twice the line thickness above the reference line. The text should never touch the reference line itself.

Leader Lines Text

BS ISO 128-22:1999 Technical drawings – General principles of presentation – Part 22: Basic conventions and applications for leader lines and reference lines

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