Mower conditioners
John Deere mower conditioners are good, tough machines. They are called MoCo's (MOwer COnditioner). The current ones have heavy duty rollers and other components. The disks (disks with knives on them) have an interlocking system, with each disk being a separate module and being removable separately. That means that you only have to pull the broken one out to fix it, not others. They are driven by gears that go through each module and transfers power to the next. That of course means that if you take one out, the ones down the line from it won't work.