These pulley wheels are the Shimano factory replacements for your XTR RD-M970 rear derailleur. As expected from XTR, the quality of the materials and design are top notch.

The 11t upper pulley wheel is oversized and then hollowed out by the teeth giving it a spoke-wheel look. It also has built-in lateral play to allow the chain to find the perfect alignment with the cassette cog. This is one of the many nuances which make Shimano shifting so sublime. The lower pulley is scalloped to save a bit of weight, then reinforced with and X style spider around the center of the wheel for rigidity.