It really shouldn't matter as long as it is the correct part number (or equivalent). I suspect that the metal is aluminium.
My engine wouldn't turn over with the plastic one, but it was used so could have been bad. Ended up just unplugging and replugging all my aluminum ones and reset the ECU after an oil change and my P0021 code went away. Thanks for the input!It really shouldn't matter as long as it is the correct part number (or equivalent). I suspect that the metal is aluminium.