These lower headset cup extenders allow you to adjust the geometry of your bike frame by increasing the effective fork length by 10mm. They allow you to do things like use a rigid fork on a suspension-corrected frame or use a fork with a shorter axle-to-crown height rather than what the frame was designed to use. They can also be used to increase the bottom bracket height and lower the headtube angle. Wolf Tooth Precision Headsets are machined in the USA out of aircraft-grade 6061 aluminum with superior sealing for protection against the elements. These ZS headsets are for frames with internal bearing cups that are pressed into the frame.
Any frame that uses a zero stack headset with a 56mm lower head tube inner diameter