Rashi on Exodus 25:27/רש"י על שמות כ״ה:כ״ז

1לעמת המסגרת תהיין הטבעת OVER AGAINST THE RIM SHALL THE RINGS BE — inserted in the legs over against the extremities of the border.

2לבתים לבדים FOR PLACES FOR THE STAVES — These rings shall be receptacles in which to put the staves.

3לבתים means for the purpose of being (to serve as) receptacles for the staves, as the Targum has it: places for the staves.