Bicycle disc brake rotors can become warped from extensive use, excessive heat, or impact. Even new disc rotors may not always be perfectly straight, causing annoying pad rub and affecting performance.

The Park Tool DT-3 installs onto any Park Tool TS-2, TS-2.2, TS-2.3, TS-4, or TS-4.2 Professional Wheel Truing Stand, and accurately gauges the straightness of any disc brake rotor while the wheel is mounted in the stand. The DT-3 features an infinitely adjustable, finely threaded locking indicator gauge that will not mar the braking surface. Works with brake rotors of any size.

Warning: California Proposition 65 

https://planet-cyclery.myshopify.com/pages/warning-california-proposition-65