Exodus 26:17-21

There shall be two tenons for each board, fitted to one another; that is what you shall do for all the boards of the tabernacle.

You shall make the boards for the tabernacle: twenty boards for the south side.

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

and for the second side of the tabernacle, on the north side, twenty boards,

and their forty bases of silver; two bases under one board and two bases under another board.