REPLACEMENT TRACKBALL - Designed for any trackball mice using 1.34 (34mm) trackball size; Such as: PERIMICE-517/717, MX Ergo, M570, Cordless, TrackMan Wheel (not include Trackman Marble), M-XT3DRBK (EX-6), M-DT2URBK, EX-G/DEFT, MA-WTB43BK SMOOTH SURFACE - The surface is treated with a special coating to provide a precise and smooth tracking performance