I don't think the 125 had any plastic gears, but there are one or two plastic gears in these models. They were early to introduce the plastc gear too, not just the free arm zigzag. I'm not quite sure on the 500 series, I shall have to look into it. I'm thinking along these lines too, I like the all metal machines, but even so the 730 has been a favorite for the way it behaves, and these machines are very much the same even if the 830 is much later these models aren't that far from each other. There are unfortunately a few 930s and 1130s with failing circiut boards or whatever goes wrong with the electronic parts. Sometimes it can be repaired, it often can, but it costs quite a bit and parts are difficult to find since they aren't made anymore. The factor of all metal gears is why I so want one of those early zigzaggers, some of them are almost as smooth as Singer 201. There is an early Husqvarna zigzag that looks nice and there is the Pfaff 130, but I have my eye on the Bernina.