Yes it is, 5% OD. Some guys were talking about dampers and strokers and it was the consensus that past 6500rpm and any stroke crank or any combination of the 2, they are pretty much mandatory. People have ran stock 6.1 dampers many times in those situations and the results are not good. Phantom oil leaks and valvetrain problems are the minor problems that occur. So I bit the bullet. One more tidbit before installing one of these, take a 1" flap wheel on a drill, I used a 120 grit, and lightly hone the inside of the hub to take the black oxide off and it will go on nice and smooth with no binding up. My crank has a keyway which these dampers also utilize as another bonus.