The early SS models had an FE3 suspension that used a 0.750 inch ball joint stub on the aluminum LCAs that mated to a corresponding aluminum hub upright. The later SS models (2008+) had an FE5 suspension that used a 0.805 inch ball joint stub on the corresponding aluminum hub upright. This difference in ball joint stub has created a lot of problems at time trying to get the correct ball joint replacement for the later SS aluminum LCAs.
The aluminum LCAs, early or late, can have the ball joints replaced - contrary to GM literature who just wanted to sell you new LCAs for more $$. The rivets can be ground off and grade 8 or better bolts can be installed with the new ball joints - bolts come with some kits.
Edit: this is the Moog PN for the late SS ball joints - K80566.
The FE5 suspension RPO code was used for all years of Cobalt production.
FE1 suspension
19-mm front stabilizer bar
16-mm rear stabilizer bar
Stamped steel front lower control arms
This was the base model suspension
FE3 suspension
22-mm front and rear stabilizer bars
Cast aluminum front lower control arms
FE3 shocks and springs
This was the mid-tier option fitted to the SS/NA and Sport trims (LE5 engine)
FE5 suspension - 2005-07 years
24-mm front stabilizer bar
FE5 shocks and struts. The springs may be different from some FE3 models.
Larger front end links
This was fitted to the SS/SC
FE5 suspension - 2008 and up years
24-mm rear stabilizer bar
NEW FE5(LNF) shocks, struts, and springs.
Updated front knuckle
This was fitted to the SS/TC