92 Regal Bolt size

Can anyone tell me what size the bolt is on the rear brake caliper mounting support on a 92 buick regal? I want to replace the rear brake pads but I need to make sure I have everything before I start. I have a socket set but I was told that the top bolt can't be removed by a socket so I may have to buy a box end wrench or opened end wrench the remove it.

i'd say it is a 17 or 18mm i'm not real sure.also some takes torx or allen wrench on the pins i always say buy a hanes manual you might even call auto zone or advanced to see what it does take..

good luck....