CST2545 (L-Trac) USB Wired High Performance Trackball (Black) - Made in the USA Width 3.75" (9.5cm), Length 6.75" (17.1cm), Height 1.75" (5cm) Ball Size: 2.25" This model does NOT contain a Scroll Wheel. However Scrolling is Possible with all web browsers and most appilcations by clicking the center button and moving the ball. Made in the USA / Model ID # CST2545 Resolution: User selectable 400, 800, or 1600 counts per inch