I need to buy a deep socket to get my stock sub's assembly unbolted. Does anyone know what size it is? I can't get anything around it...

 

a deep socket 10mm and an extension should do the trick!

 

Yeah the 10mm is the most common size. Hell you can practically dismantle the entire car with a 7mm, 10mm, and 13mm sockets.

 

IMO- A 9/32 fits the bolts a little snugger than the 7mm but maybe thats me.
In any case bothe the above posts are right, 75% of the bolts in the car are 10mm right down to the bolt holding the leads on the battery down.
(this was my suttle way of reminding you to disconnect the neg lead before you unplug anything)