1,Desktop optical metal trackball with 38mm diameter 2,Water/dust-proof,meets IP65 rating 3,With click buttons and palm-rest Key Features ... Force for Keys: 80g nominal• Lettering: raised graphics with scrape-resistant printing ink• Trackball diameter: 38mmOperation system• PS2: Win NT4, 98SE, 98ME ... .00 mm x 46.50 (LxWxH) IP65 Desktop Optical Metal Trackball mouse with 38mm doa,eter