I liked the solution of a simple zip tie to stabilize the y axis pulley on my Wanhao i3 duplicator...but...it felt too makeshift.

So I created this. The stabilizer slides over the existing front panel and then the bottom clip snaps on to hold it tight. The M5 shoulder bolt through the pulley and into the existing pulley mount holds it in place laterally. It doesn't require any screws so you don't have to drill any new holes. You do need a new, longer M5 screw though; I used an M5-40mm Hex Cap Socket shoulder screw which turned out to be a little too long, but who cares since it works quite well with my Duplicator i3. Hope it does for yours as well.