Exodus 26:18-21

18You shall make the boards for the tabernacle [in the following quantities]: twenty boards for the south side.

19You shall make forty silver sockets under the twenty boards, two sockets under each board for its two dovetails, and two sockets under another board for its two dovetails;

20for the north side of the tabernacle there shall be twenty boards,

21and their forty silver sockets, two sockets under each board.