You need the mounting brackets for a 13 Base car to mount the aftermarket speakers. I pulled this quote from another thread
You don't need these spacers if you have the base. You DO need these if you have the premium with the Shaker. I had to order these from a 2010 GT for my 2014 premium to allow the aftermarket speakers to fit.
2014 Ruby Red V6 Premium w/pony package, Magnaflow Street axle-backs, LED license plate light, LED interior lights, Strip LED trunk lights, MMD Hood struts, SCT X4 Tuner with Steeda tunes for life, Boss 302 strut tower brace, OEM extended range remote start, Raxiom Navigation.