For current Airtronics product try taking a look at the on line catalog. Servo descriptions, gear construction, bearings/bushings, sizes, weights, speed & torque ratings at both traditional voltages, in analog and digital sections (and others), pretty much everything the other guys list seem to be there.

For older product, try the Wayback Machine, archive.org. Typical of that service, not all versions are complete. But with a little searching one can usually discover a lot of information including most of the aforementioned servo specs. I don’t believe the 357 is listed or described as a digital servo. Doesn’t mean its not a quite good servo of course.

The Z suffix simply means it has Airtronics version of the sort of standardized servo connector. As opposed to the proprietary/different connectors that many brands once used. Over time they have dropped the use of the Z on some of the newer product I believe.