I believe that is a 3/8 Allen key.
it's a 3/8 wrench for both 2003 and 2004 caliper.
All Cavaliers from '94 to '03 used 3/8 Allen key on calipers.
9mm Allen wrench
I believe that is 7mm Allen key.
I believe that needs a 3/8 Allen or some models, 7mm Allen.
Most likely a 15mm wrench. Unlikely to be Allen in that vehicle.
You need a 3/8 Allen Wrench
That would be a 7mm Allen.
Not likely to be Allen key, try 15 mm regular wrench
Metric Allen wrench.