My girlfriend, the darling over at Spleen Chronicles, was lamenting the lack of line styles in Illustrator today, specifically the ability to put a double-line stroke on a path. I being a big fat cheater, gave her a way to get the effect she was looking for at the expense of the inside area between the two lines not being transparent. After the break you’ll find my walkthrough for the double-line stroke, screenshots are from Illustrator CS4, but it is possible to achieve the same effect in CS3 and perhaps earlier.
To start off, draw a line with the pencil tool or create a shape.
Increase the width of the stroke to accomodate the width of both lines plus the gutter between them, I used 5pt.
Next you need to add a second stroke to the line to serve as the gutter. Click the Add New Stroke button (1), then change the color of the stroke to match your background (2), and set the width to the width you want the gutter (3). You should now have the appearance of a double line stroke!
Step 4 (optional)
If you’re noticing and annoyed by a faint line at the end, you can change the cap on the gutter stroke to a round cap and it will disappear.