There are different different used depending on the exact placement. If it is only holding one bracket directly to the water pump it is the shorter one. If it’s holding multiple brackets like in an air-conditioned car it would be the longer one
Several different head markings, common is RBW and also use a lot was one with a F in the center and a third one has no marking in center of bolt however all three are the same type flanged head
There are also differences in the diameter of the flange washer. Ones used to hold an adjustment in slot have a wider built-in washer