The CPITN probe has a ball end of which diameter & marking at what level:
0.5 mm diameter ball and marking at 3,5,8 and 11.5 mm. 1.0 mm diameter ball and marking at 3.5, 5.5, 8.5 and 11.5 mm. 0.5 mm diameter ball and marking at 3.5, 5.5, 8.5 and 11.5 mm. 1.0 mm diameter ball and marking at 3,5,8 and 11.5 mm.