30 X 72 X 19mm
C4 bearings have additional internal radial clearances to allow expansion in high speed / temperature environments.
Unless the bearing you are replacing specifically says C4 on it then you should not replace it with a C4 bearing.
These bearings are supplied pre-filled with grease, "/5k" refers to the grease: Multemp SRL (-40 deg C to +150 deg C)
6306 ZZ C4/5K NTN Metal Shielded Deep Groove Ball Bearing