Thank you for your hard work.
@Abetillo You raise a valid point which disturbed me somewhat. But it seems like Japanese swords (katanas) might have at the end of their era been modernized into using copper handles and permanent mountings. So it might be a reference to such swords being somewhat sturdier/harder to break than earlier katanas with removable handles/hilts.
..or it's a mistake in translation, but one clearly very easy to make?