Thanks looks like a 5 and 1/4 ? do you have nav? BTW it looks like the mount of the enclosure uses the 6x8 of the previous years.
No nav. This mount will not fit a 6x8 without a bunch of modification. I think I paid $12 a piece for the speaker mounts that are made to fit a 6x8 speaker.
Here is the link for the driver and passenger side speaker mounts
Item #7 in each diagram
2010 FORD MUSTANG Parts - Tousley Ford Parts Depot
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2010 FORD MUSTANG Parts - Tousley Ford Parts Depot