11:
You're welcome. I gave a rather incomplete answer earlier, but thought you sounded like you needed the brush rather than a long tutorial.
I made a mistake, or rather left out the detail that the unstroked unfilled rectangle has to be the back most object of the brush.
Try this:
Draw a square, make it 1" wide and tall.
Copy (Ctrl-C). Paste in Front (Ctrl-F).
Scale 200% width, 100% height.
Direct-Select the right hand side anchors. Hit Ctrl-Alt-V (Average), Both (default).
Select the square, remove stroke and fill.
Fill the triangle with something nice, maybe a Fire Red. Stroke, hmmm, Black!
Select both, and drag the whole thing onto the Brushes palette. Now, a dialog comes up, make it a Pattern Brush, all default (except maybe set it for Tints in the color mode box).
Make some brush strokes. Note how your triangles overlay each other. Measure from one tip to the next, you'll find roughly 1", the brush "unit" length.
Bert