Sforno on Exodus 25:12/ספורנו על שמות כ״ה:י״ב

1פעמותיו, the corners at its outer edges.

2ושתי טבעות על צלעו האחת, the side, wall of the Ark, is called צלע. G’d had commanded therefore that these rings be attached at the four corners of the Ark. G’d therefore commanded that there were to be four such rings at the four corners. Furthermore, G’d commanded that they not be attached along the short sides of the Ark but along the long sides of the ark. [this contradicts the commentary of both Rashi and Rash’bam. Ed.]