C. F. Keil and Franz Delitzsch on Exodus 26:25-27

Exo 26:25-27

Sixteen sockets were to be made for these eight boards, two for each. - Exo 26:26-29. To fasten the boards, that they might not separate from one another, bars of acacia-wood were to be made and covered with gold, five for each of the three sides of the dwelling; and though it is not expressly stated, yet the reference to rings in Exo 26:29 as holders of the bars (לבּריחים בּתּים) is a sufficient indication that they were passed through golden rings fastened into the boards.