The flexplate is used on an automatic transmission. A flywheel is used on a vehicle with a manual transmission. It's where the clutch is mounted.
@missileman .. thanks, I looked up a u-tube vdo which shows the difference.
(To see the utube vdo , Google transmission flexplate, it should be right at the top, titled “How flexplates work vs flywheel”)
Edit: After watching the vdo, I still don’t understand why it flexes ! … lol … says something about preventing it from “bottoming out”, but what does that mean? and why would it be a problem on an automatic and not a manual? Car parts are sometimes very puzzling to us auto-repair diy’ers.
@Feasle … metals have a coefficient of expansion ; i.e. they expand and contract w/temperature. The gears on the starter motor need to mesh perfectly with the teeth on the flexplate (for an automatic, or flywheel if a manual xmssion). A flexplate is like a big flat disc-like-thing. The teeth are on the circumference. When the flexplate is cold, it will have a smaller diameter, so the starter gear will have to reach further to engage with the flexplate teeth. If the flexplate teeth are already ground down a little from before, then with the cold temperature contracting the whole flex plate, the starter gear might not quite reach the teeth. And if the starter gears don’t reach far enough to robustly engage, the gear will slip, and make a grinding noise…
edit: I’ve heard of people shimming their starter motors to address this problem, provided the flexplate/flywheel teeth are in working order.