How to create a Top view fence design for the line tool

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You may use an Art Brush with non stretching ends consisting of the following parts (see it horizontally):

1) A long filled rectangle with a width corresponding to the length (not the exact length) and a height equaling the thickness of the fence boards;

2) A filled square with the pole size at each end below 1), Grouped;

3) A copy of the end square Group from 2) moved upwards by the square height changing the Fill to None;

4) Group 1) - 3) and turn it into an Art Brush with non stretching ends corresponding to the squares, see explanations here:

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Made this way, the centre of the Art Brush will be below the fence boards and above the poles.

With this, you can create each stretch of fence with a 1pt line with the Line Tool, and you can make stretches fit together as follows, startíng with coinciding end Anchor Points:

A) For continuous stretches create each stretch with the Line Tool, each set of coinciding end Anchor Points will have a double set of poles, but you can stretch either of them by the pole square size from the other end (or Direct Select and Move the end Anchor Point in question) to overlap to hide one pole under the other;

B) For stretches meeting at a right angle with the poles on the outside, the stretches will join fine as they are; the same applies to other angles;

C) For stretches meeting at a right angle with the poles on the inside, the stretches will join less nicely with the fence part unclosed, but you can stretch either of them by half the pole square size from the other end (or Direct Select and Move the end Anchor Point in question) to close the fence part; other angles will give a bit more challenge.