The UAX7 was designed to cater for 800 subscribers, and so would be installed in locations that were too large to have UAX 6 or 13's. The exchanges were built around the Pre-2000 type selector, which was used for linefinders, group and final selectors.
They were the first UAXs which had four digit numbering, the first digit being absorbed by the group selector, the transmission bridge is also, unusually, in the first selector.
Tones were provided by tone drum ringing machines, which allowed the UAX7 to be easily identifed until their demise.
I have preserved a UAX7 exchange in my collection. I have three racks, which is enough to give 100 lines. The racks are an Aa unit, B unit and a D unit. I will be adding photos of these to the individual rack pages in due course.