וַיִּצֹ֞ק אַרְבַּ֧ע טַבָּעֹ֛ת בְּאַרְבַּ֥ע הַקְּצָוֺ֖ת לְמִכְבַּ֣ר הַנְּחֹ֑שֶׁת בָּתִּ֖ים לַבַּדִּֽים׃
And he cast four rings for the four ends of the grating of brass, to be holders for the staves.
Read kabbalistic (mystical) interpretation of Exodus 38:5: and classical mystical sources.