יחזקאל מג:יג פירוש: רש״י

And these are the measurements of the altar as he explains further (verse 17): “fourteen [cubits in] length by fourteen [cubits in] breadth.”

in cubits; the cubit, one cubit and a handbreadth with a cubit of six [handbreadths], which is a cubit and a handbreadth, [judging] by a cubit of five [handbreadths].

but the base one [ordinary] cubit but its base is measured with an ordinary cubit, which equals five [handbreadths]. The word חֵיק is related to חֵקוּי, permanence, it refers to the one cubit. The cubit is the ordinary cubit, not a cubit and a handbreadth, which is the cubit of six [handbreadths]. So too did we learn in Menahoth (97b) that the base, the circuit, and the horns are measured with a cubit of five [handbreadths].