Thread tap/chaser? The nut is pretty loose, that's why the bolt has the pilot on the end.

GM may have the bolt in stock, sometimes they surprise.

Nope, K6698, rockauto lists it as the heavier duty problem solver version for the hhr. It looks better with no voids.
Your link doesnt list the hhr, just cobalt, same with the rockauto listing. If you say it fits i will take your word and try to get an exchange. It looks to be a spherical joint?

It is

gio-outdoors: Upgrading Chevy HHR Lower Control Arms

Ok, ordered those.
I did manage to get the other control arm on.
The brand new bolt wouldnt even start, not a good sign, so I used the old bolt and crossed my fingers against crossing the threads. I lined it up and used fingers then a 3/8 ratchet so I could get a feel if it wasnt being nice about it. The final torquing sequence was more suspenseful than Id like, but it did hold.
Once that arm was on it also helped with the swaybar clearance on the other side. I immediately felt the difference in driving. No more loose knocking, initial hesitation in braking, loose steering, wobbling under acceleration.

It was a pain for me to get the rear bushing lined up but, with patience I got everything lines up. Twist and wiggle its way in there, and it shouldnt give resistance going back in; if the bolt is resisting something isnt lined up.

Sometimes the weight of the cradle will cause one side to bind a bit if you support the body and not the cradle with the jack stand .

Just replaced control arms using this guide, A+ instructions. The only thing I'd add is that the 13/16" rear bushing bolt cannot simply be loosened, you need to get a 13/16" wrench on the top nut to prevent it from just spinnin. Very tight squeeze but totally doable, I was reading other threads where guys thought their bolt was just fused which may be true in their cases just don't forget about the top nut otherwise you'll be drilling out the bolt for no reason. Just hit 250,000 miles w original motor on my HHR :)

The nut is supposed to be captured. Somebody must have modified yours.

Interesting, good point not original owner and not original arm I replaced.

Just curious. How did you know it wasn't the original LCA ? The originals are cast aluminum and so are the correct replacement ones. They both should look identical.
Now, an incorrect replacement would be a stamped steel arm, generally painted black. Those were usually found on the Cobalts and not recommended for the HHR's.