For the joinings — that is, the girders or cramps; pieces of iron used to join beams or stones together.

David gathers craftsmen and accumulates materials for building the house of God.

And David commanded to gather together the strangers that were in the land of Israel and he set masons to hew wrought stones to build the house…

And David prepared iron in abundance for the nails for the
doors of the gates, and for the joinings…

Following the terrible judgment inflicted on Israel for David's sin, God pointed out the place where he wanted the temple to be built. After this, …