וְעָשִׂ֣יתָ קַרְנֹתָ֗יו עַ֚ל אַרְבַּ֣ע פִּנֹּתָ֔יו מִמֶּ֖נּוּ תִּהְיֶ֣יןָ קַרְנֹתָ֑יו וְצִפִּיתָ֥ אֹת֖וֹ נְחֹֽשֶׁת׃
Y harás sus cuernos á sus cuatro esquinas; los cuernos serán de lo mismo; y lo cubrirás de metal.
Rashi on Exodus
ממנו תהיין קרנתיו ITS HORNS SHALL BE OF THE SAME — i. e. he shall not make them separately and afterwards attach them to it (to the altar).
Sforno on Exodus
קרנותיו, a feature of all altars, as were the shovels and the basins for the blood as receptacles.
Rashbam on Exodus
ממנו תהיין קרנותיו, integral parts of the structure, not something superimposed.