Rashi on Exodus 28:20/רש"י על שמות כ״ח:כ׳

1משבצים זהב יהיו SET IN GOLD SHALL THEY — the rows — BE במלאותם IN THEIR SETTINGS — surrounded by gold settings in depth of such a size that each shall be filled by the thickness of the stone. This is the meaning of במלאותם, “in their fillings”: of such a size as will be filled by the thickness of the stones shall be the depth of the settings, neither more nor less.