Numbers 4:28-33

The Gershonites and Merarites are superintended by Ithamar, Aaron’s younger son, who had already had the oversight of the tabernacle in its construction Exodus 38:21. Thus, readily do the permanent offices of the leaders of the Israelite community spring out of the duties which, under the emergencies of the first year of the Exodus, they had been led, from time to time, to undertake.

Numbers 4:32

By name ye shall reckon the instruments - Or, assign them to their bearers singly, and “by name.” These “instruments” comprised the heavier parts of the tabernacle; and the order seems intended to prevent individual Merarites choosing their own burden, and so throwing more than the proper share on others.