Kensington 4-Button Expert Mouse USB/PS2 Trackball USB and PS2 support for PC users and USB Macs for easiest connectivity Large ball with stainless steel bearings give smooth, precise tracking and maximum durability Symmetrical, comfortable design features a classic color tone that complements most PCs Customizable buttons provide single-click options to repetitive tasks The Kensington satisfaction guarantee - 5 year warranty, toll-free technical support, 90-day no risk trial