Hi, I remember someone talking about this topic,but I can't find the dang thread! Anyway I sold a friend my timing belt kit which had a single and double bearing idler. Does the double go on top and the single goes below? (red one).

 

they are actually interchangeable physically speaking.

 

but you got it right, the double bearing idler goes up top, the single on the bottom.

Ok perfect thanks!

That looks correct as pictured. The upper one takes more load hence the double row there. Ordering the single row from Subaru now gets you a double row as a superceded part. The single row has been known to fail in the double row position.