It is required to bond conductive materials enclosing the conductors (such as your flex). You need to connect the flex to the ground wire via some listed method. Using the appliance or coincidental contact with the grounding conductor isn't one of them.

That should say "approved" rather than "listed" (of course listed ways of doing it are approved).

ronnataile-
Thanks for the response. However, humor me one more time. This 42" long metallic flex runs only from the appliance to the plastic junction box where the single power cable is; and the flex is enclosed in the wall space at the back of the oven. The only thing connected to this junction box is the breaker. I would think the flex could only get energized if the frame it is connected to got energized, and that frame is grounded. I'm not saying you're wrong...I just want to understand completely. Thanks.

The code is what it says. There's no provision for reasoning that you don't need the bonding. The wiring inside the flex might fail, someone might drill a hole through the flex, whatever, the flex might become engergized. It needs to be bonded to the ground and it can't be relied upon to do so through the frame of the appliance.

ronnatalie-
Thanks for the additional explanation. When putting on a bonding bushing, is that sufficient to lock the nipple into the box, or does it need a locking collar on top of that?

Can you site the nec code that states what you've said ron? As i read the code no additional bonding is required that a lock ring connector unless using a concentric knockout. 250.97