Hellwig 981 EZ Helper Spring vs Hellwig 979 EZ Helper Spring ?

Hi, I've decided to add a helper spring setup to my 2013 Tacoma 4x4 base 4-door.
I've looked on the Hellwig site, and other online sources, I can't determine what the difference is in these two Hellwig part numbers. I wanted to try and figure it out this weekend, (Hellwig is closed) Anyone know the difference?

Thanks PB in TN

 

I just installed the 981 on my 2012. If you see below...the 979 is for 05-11. The 981 fits all 05-15.
The 2012-2015 have one shackle near the gas take that mounts sideways, and the 05-11 does not require this, but can be mounted this way.
I am pretty happy with mine so far...just trying to adjust to find the sweet spot.
I had them tighten down a lot when I first installed, and the rear end was noticeably stiffer. I drove over my usual Rail Road tracks that always make me hit my bump stops...and they did not hit. It raised the rear about 1"
So I loosened them up and rear was back to "stock feel" (and height), but now I hit the bump stops on the RR tracks. So I am still tightening a little each day, trying to find the spot where it isn't stiff and I don't hit my bump stops. But even the Stiffness isn't that bad...I am just picky.
Overall very happy with them...just waiting to carry something heavy...but nothing planned in the immediate future.



http://www.sdtrucksprings.com/index...&make_select=654&model_select=8835&x=112&y=13