User blog comment:12th Supernova/750 chapters is a LOT/@comment-3425840-20140618154341/@comment-1595565-20140618184602

Only the cuffs themselves have seastone in them. The chains aren't. There is enough seastone in them to nullify fruit powers and make them submissive, but not enough to the point that the wearer feels completely weak. Franky's beam would make sense since it's a laser of some kind, which is the normal method for cutting diamond.