2012 Sportsman 400/500 and EFI Tractor Service Manual 9923412, Page 359Get this manual
BRAKES REAR BRAKE DISC
Inspection
1Visually inspect disc for scoring, scratches, or gougesReplace the disc if any deep scratches are evident2Use micrometer and measure disc thickness at different points around perimeter of discReplace disc if worn beyond service limitReplace the disc if runout exceeds specifications
= In mmBrake Disc Runout Service Limit: .010".254 mm