1,Desktop optical metal trackball with 25mm diameter 2,Water/dust-proof,meets IP65 rating 3,With click ... and palm-rest Key Features- Small optical metal trackball(dia:25mm),made of abrasion-resistant stainless steel- Specially designed to operate ... nominal• Lettering: raised graphics with scrape-resistant printing ink• Trackball diameter: 25mmOperation system• PS2: Win NT4, 98SE, 98ME, 2000,XP• USB ...