Based on what people have said, hat seems to be most common. Maybe top and bottom are the same. I wouldn't say they were any more common than that though. And the back in RSC Jagex said chance of a D med off fire giants was 1/16k, they also said that was the same chance as getting a chain off dusts I believe. Anyway, the point behind they're nowhere near as rare as dragon chain from dust devils, not even close. If they are the same drop rate, I'd say 1/512 sounds right.