John Gill Commentary 1 Kings 7:34

"And there were four undersetters at the four corners of each base: the undersetters thereof were of the base itself." — 1 Kings 7:34 (ASV)

And there were four undersetters to the four corners of one
base
Or pillars, as in (1 Kings 7:30)

and the undersetters were of the base itself ;
they were cast together, and of the same piece of metal with it.