וְהָי֣וּ תוֹאֲמִם֮ מִלְּמַטָּה֒ וְיַחְדָּ֗ו יִהְי֤וּ תַמִּים֙ אֶל־רֹאשׁ֔וֹ אֶל־הַטַּבַּ֖עַת הָאֶחָ֑ת כֵּ֚ן עָשָׂ֣ה לִשְׁנֵיהֶ֔ם לִשְׁנֵ֖י הַמִּקְצֹעֹֽת׃
that they might be double beneath, and in like manner they should be complete unto the top thereof unto the first ring. Thus he did to both of them in the two corners.
Read kabbalistic (mystical) interpretation of Exodus 36:29: and classical mystical sources.