d15b7 Crank pulley

OK so ive come to an issued with this style crank pu8lley. I have my own z6 which the pulley can be held in place with a 50MM hex tool sold on ebay and what not. now i thought it would be the same on this d15b7. and what i have is similar to this.. How and what tool can be used for this to hold this sucker in place.. ..??

