Shock bolt size

[mturnerua]

I'm about to replace my rear shocks on my 07 Denali. I've got to buy a ratchet wrench for that tight upper one and I wanted to know what size I need. I'm guessing its a 20 or 21 but wanted to know for sure. Also if anyone has any tips on getting the top bolt off let me know.

Thanks

 

[08grey]

Not sure the size but get a couple of extensions.