Hi guys I'm trying to chang my belt tensioner, getting the belt off was easy , now i'm stuck , the one bolt that attaches the tensioner to the brackek is round or looks round , there is a hole in the center of it , but when i try to put a hex in it will only go in 5 to 6 mill , I don't think that is the correct way ... any help would be apprecated Thanks, 2000 f150 , 4.2 with air.

 

is it a torx?

 

I don't have any so i can't say for sure .