Similar to the TJET magnets these were often a bit hard to pin down for strength. That said the 502 magnet generally was the best . 502's were the red and light blues and the replacements sold on cards were red and blank /black . Best of the 502's on the cards then were those with the dimples as the dimple denoted that they were fully oriented magnets similar to those found in the Super 2 . No rhyme or reason but oddly the carded mags had a mix of dimples and non with usually many many more non. Anyway ...hope this helps ya out in the end !I see all different color types of magnets in my non magnatraction cars.in general which colors are the best?