The spacer for the Shimano XTR CS-M9100-12 cassette is a thin spacer made of plastic (resin), which prevents possible noise development. As a so-called low spacer, it is mounted between spider arm and freehub body. Shimano has delivered it with all CS-M9100-12 since the end of 2018. It is not necessary for the XT and SLX 12-speed cassettes, as these, like the XTR successor model CS-M9101-12, are equipped with a pre-installed adhesive ring.