Exodus 26:21

You shall make twenty boards for the tabernacle, for the south side southward.

You shall make forty sockets of silver under the twenty boards; two sockets under one board for its two tenons, and two sockets under another board for its two tenons.

For the second side of the tabernacle, on the north side, twenty boards,

For the far side of the tabernacle westward you shall make six boards.

You shall make two boards for the corners of the tabernacle in the far side.

They shall be double beneath, and in the same way they shall be whole to its top to one ring: thus shall it be for them both; they shall be for the two corners.