30 X 72 X 19mm
C4 bearings have additional internal radial clearances to allow expansion in high speed / temperature environments.
GJN REFERS TO HIGH TEMP GREASE IN THE BEARING
Unless the bearing you are replacing specifically says C4 on it then you should not replace it with a C4 bearing.
6306 ZZ C4/GJN Metal Shielded Deep Groove Ball Bearing