the 9.86 are the correct ones. There are 2 options because of stupid parts books.
The Moog part number for the 9.86 inch part end with 12, somebody in the waybak decided that meant they were 12 inch. Then asked "do you want the 12s or the 10s?".
The part numbers are so different I doubt they were meant to be interchangeable.
I don't think it makes enough difference to argue about. My experience was that the 12 inch parts caused a problem by shifting the sway bar laterally, maybe the sway bar stays were already bad and just a coincidence.
The 12 inch part reduces the ground clearance a bit because the ends of the bar are 2 inches lower. As long as the 2 sides are the same the sway bar functions the same.

 

I changed the sway bar links,lca's,hubs,rotors,intermediate shaft, and still had the clunk.Of course the last thing I changed was the sway bar bushings and poof! Clunk gone.They looked fine but obviously weren't.

 

Looks can be deceiving!

 

That's interesting! Due to all of the previous clunking cars on this forum when I first heard it, that was the first thing I changed, but with no difference. So, the next step is to change the Moog Links to the Delphi Links. But, since I'm changing that, I'm curious which Sway Bar Bushings you put on, because I put on Moog K201303, but I see there is also AC Delco Professional 45G10046. I might have those changed out back out while I'm at it.

 

I have the GM Genuine installed in the BlackSwan, I see Delphi has bushings also, I have not tried those… yet.

 

There are 2 different sizes of sway bar used on HHRs, measure yours to know which you have.
They are METRIC, SAE is not close enough. Genuine GM are not expensive.

 

In a 2010 1LT 2.2 litre, then chances are you have a 25 mm sway bar

 

25mm is smaller than 1 inch by enough to cause a problem.

 

I know, the 1” polyurethane bushings rattled like crazy after a rain.
1” equals 25.4 mm , close but no cigar!!

 

About 1/64” wrong