Albert Barnes Commentary Job 41:17

"They are joined one to another; They stick together, so that they cannot be sundered." — Job 41:17 (ASV)

They are joined one to another - literally, “A man with his brother;” that is, each one is connected with another. There is no natural fastening of one scale with another, but they lie so close and compact that they seem so to be fastened down on one another; see Bochart on this verse.

It is this which makes the crocodile so difficult to kill. A musket-ball will penetrate the skin under the belly, which is there less firmly protected; and accordingly the efforts of those who attempt to secure them are directed to that part of the body. A ball in the eye or throat will also destroy it, but the body is impervious to a spear or a bullet.