Radiator cap does not mount on the radiator, it mounts on the expansion tank. The cap does not come with the tank. But the Behr radiator does come with the blue plastic drain plug. Only reason i know is I just bought both this week and am doing the install Sunday.
1995 525i 5 speed - sold at 225,000 miles
2002 530i 5 speed - 160,000 miles