As for the sons of Merari, you are to number them by their clans and families,
We have here the charge of the other two families of the Levites, which, though not so honourable as the first, yet was necessary, and was to be done regularly. 1. The Gershonites were charged with all the drapery of the tabernacle, the curtains, and hangings, and the coverings of badgers' skins, Num 4:22-26.
Commenting on Numbers 4:21-33
And the pillars of the court round about, and their sockets, and their pins, and their cords,.... These belonged to the court of the tabernacle; the pillars were what the hangings were hung upon, and the sockets, into which the pillars were set, and the and cords, with which the hangings were fastened; see Exo 27:9, with all their instruments, and with all their service...
As for the sons of Merari--They carried the coarser and heavier appurtenances, which, however, were so important and necessary, that an inventory was kept of them--not only on account of their number and variety, but of their comparative commonness and smallness, which might have led to their being lost or missing through carelessness, inadvertency, or neglect.