I have a K-40, the magnet is about 6" dia. will hold in 120 mph wind. one piece of advice. DON"T leave it in one place for a long time. as the article above stated, about fading paint. mine cause paint ripple or orange peel under the magnet. not to bad but noticeable with your hand. I expect this in time, will cause the paint to peel in this area.
just my penny's worth.
Marv.