User blog comment:12th Supernova/750 chapters is a LOT/@comment-3425840-20140618154341/@comment-3425840-20140618165221

For your info - diamond, though hard is reasonably brittle. It can not be cut by anything solid except itself, however breaking it is not all that tough.

As for the cuffs, well they are tough alright but so tough that they would still need the kay to break them when people as strong as Luffy or Zoro are around? A bit hax.