CST1550 USB-PS/2 Wired Ambidextrous Ergonomic Black Trackball - 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 Buttons: 2 (programmable) + Middle (Draglock) Made in the USA Installs using PS/2 or USB interface port.