Go to Crutchfield.com and they will have all of the sizes of your factory size speakers for your car.
You don't need factory speakers. Just buy the same size speakers and install.
5 1/4". I believe that 6.5" can fit there also but I'm not exactly sure how.
6x8
The dash has 3x5 and the door and rear deck speakers are 6x9. Enjoy. ChicagolandAreaModernMopars . com
2006 E250 speaker size is 6x8"
6x8
6x9's
4in speakers in the door and dash
6x8
Front speakers Front Door: 6-3/4" factory speaker note Far rear speakers Rear Pillar: 4x6" factory speaker note
2006 Ford F-150 Pickup SuperCrew Cabwith factory subwooferFactory replacement info:In-dash stereo 7-7/8" depth; Size code DD,E,F3 Front speakers Front Door: 6x8" Rear speakers Rear Door: 6x8" Far rear speakers Behind Seat: 8"