i had 5.25 on there but the sound was not clear. what i did was changed to 6.5 mb quarts pce216.

first i removed the factory speaker. then with a heat gun i removed the factory speaker from the factory speaker pod. now, the 6.5 does not have a perfect fit. i used a dremel to shave around the plastic rim on the mb quart to have a tight fit with the factory pod.
try to protect the speakers voice coil, so no plastic junk lands in side. i worked with a plastic bag, and worked small areas at a time..... next
i used cloth tape inside the pod where the speaker sits. i did a few layers not a lot, also before you use the tape drill your screw holes... the tape gave the speaker and the pod a more tighter grip when screwed...