Yep, the term "knock-off" only applies when the spinner is a heavy cast metal piece, threaded, and is the only thing holding the wheel to the hub (hence the term "knock-off wheels" because you can remove the wheel simply by spinning off the center, using a rubber hammer to get it loose. Corvettes had such wheels, and they are derived from racing applications). An ornamental center ornament like the one on the '05 V6 Mustang would be referred to as a "spinner", not a "knock-off". Early Mustangs (65-66) could be ordered with spinners mounted to deluxe wire caps, or even the standard caps. It was a 3-pronged spinner, similar to what we're talking about here, and they were called "spinners" back then as well. Spinners on Mustangs go way back to the beginning heritage-wise.