Product review (5 stars): Repairing the Whirlpool Duet Dryer Model # wed9400sw2
This kit was just what I needed to fix my Whirlpool Duet Dryer Model # wed9400sw2.  This pack of parts was a MUCH better deal than the same parts and package on Sears Parts Direct.  This was listed as a Prime item, so shipping was free and I received it in about 36 hours (Sears Parts Direct wanted shipping of about $7-$10). As far as the quality of the parts, these were a PERFECT replacement of the factory original parts that were in the dryer. It included the four rollers, the belt, idler pulley (with washer), and nine triangle washer clips (two for each roller and one for the pulley).

A few tips/advise for installation: For the
(1) DO NOT OIL THE ROLLERS.  These rollers are self lubricating, and are a great fit, oiling these will cause dust and lint to build up and cause the roller to fail early.
(2) For the model wed9400sw2 (at least), it is best to keep the old pulley washer on and to add the new washer over top of that one, and then slide the pulley on.  This gives you a proper gap.
(3) This job requires you to take apart the dryer quite a bit, so before you replace the parts, take time to really clean the inside of the dryer.  Use a vacuum and crevice attachment to pull up all of the lint and dust that is all over the inside of the driver.  After all is vacuumed up, take a DRY clean cloth and wipe everything down.  You will have it looking like new! As you reassemble the dryer, wipe down each component.
(4) There are YouTube videos available that will detail how to do this job. I had never done this job before and I am mildly mechanically inclined.  This took me about 4 hours to do from start to finish (a lot of that was cleaning).

Good luck with your DIY repair project!