Exodus 26:15-19

And thou shalt make boards for the tabernacle of shittim wood standing up.

Ten cubits shall be the length of a board, and a cubit and a half shall be the breadth of one board.

Two tenons shall there be in one board, set in order one against another: thus shalt thou make for all the boards of the tabernacle.

And thou shalt make the boards for the tabernacle, twenty boards on the south side southward.

And thou shalt make forty sockets of silver under the twenty boards; two sockets under one board for his two tenons, and two sockets under another board for his two tenons.