Bars of shittim wood. To give greater stability to the structure, to keep the boards in their places, and to prevent there being any aperture between them, five bars were to be made for each side, and the same number for the end, of the mishkan, which were to be passed through rings attached to the boards—one at least to each—and thus to hold the boards firmly together.
The middle bar in each case was to extend the whole length of the enclosure (Exodus 26:28), and thus in two cases to be thirty cubits, or forty-five feet long. The exact length, and the disposition of the other bars is not indicated; but it is with reason conjectured that two were above and two below the "middle bar" that all were horizontal—and that each coupled together one half of the boards of each side.
The length of each was probably fifteen cubits; and the ends which reached the two comer posts at the back ran into the corner rings, which were shaped so as to receive the two bars (see Exodus 26:24).
It is not said whether the bars were inside or outside the mishkan; but the best authorities suppose them to have been outside.