Product review (4 stars): My experience
expensive shipping for such a little 1 oz part.  Well packaged, though, arrived in perfect condition.

I learned the hard way, feed the track through the wheels and THEN clip it on.  A channel-lock sliding wrench works well for snapping it on the track.

 I wanted to order 2, but they wanted to charge double the shipping, and it wouldn't have cost them any extra for the shipping.