Trouble with new tensioner

I feel like I'm probably being dumb here so apologies in advance. On a 2005 Tucson, I had no problem using a 3/8" socket wrench to push my old tensioner down and remove the drive belt. It turns out the belt, tensioner, and idler pulley need replacing so I just bought ContiTech kit ADK0020P from RockAuto which includes all of those things:

More Information for CONTITECH ADK0020P

The kit came yesterday and I'll be damned if I can budge the new tensioner! I haven't tried putting it in the car yet but I even tried getting it in a vise and using my 3/8" wrench on it and I can't seem to get it to move. I don't see any retaining clips or anything obvious that I would need to remove. Like I said, am I just being dumb here?

Thanks,
tim