Exodus 26:26

(26) Bars of shittim wood.—The object of the “bars” was to hold the “boards” together, and prevent there being any aperture between one board and another. They were fifteen in number, five for each of the three sides of the boarded space. The “middle bar” on each side was to extend from end to end of the tabernacle (Exodus 26:28), the four bars above and below being shorter, each coupling together probably one-half of the boards of its side. The bars were passed through “rings” attached to the boards (Exodus 26:29), each board having at least one such ring. It is probable that they were placed outside the tabernacle walls.