I checked them out, and the labeling says it works for 5.25S and 6.5s. I believe there are two types of 5.25, and it takes the slightly larger woofer frame one. If you look at a Crutchfield catalog, they lightly talk about this. From what I see, they are plastic adaptors. They are made by the same company that you usually see that make the generic radio surround/harness kits for the car's head unit opening. Now that you mention it, it does seem strange to they say you can fit a 6.5 diameter, when the smallest part of the 5x7 spec is the 5" part. But that's what it says. Jon