Exodus 36:24 (KJV)

One board had two tenons, equally distant one from another: thus did he make for all the boards of the tabernacle.

And he made boards for the tabernacle; twenty boards for the south side southward:

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

And for the other side of the tabernacle, which is toward the north corner, he made twenty boards,

And their forty sockets of silver; two sockets under one board, and two sockets under another board.