2006-2009 Honda TRX680 (TRX 680 FA-FGA) Factory Service Manual, Page 420Get this manual
BRAKE SYSTEM REAR BRAKE DISC INSPECTION Visually inspect he disc for damage or cracksM easur the brak disc thick ness at seve ral po ints
SERVICELIMIT: mm 10.2 in ]
Replace the brake disc if he smallest measurement is less han he service lim it
Check the rake isc tor arpag eSERV ICE LIMIT: 0.5 mm (0.02 in]
Replace the bra ke di sc if the wa rpage excee ds he service limit