I am trying the Denso IT16TT (4713) on my Towncar and it works fine. Panthers traditionally require 0.54 inch gap (1.4 mm). The Denso plugs come in at 0.40 preset from the factory, and I have verified that. I am confused after all the reading I have done as to whether I need to re-gap those or just leave them be. Hence, my request for the collective wisdom, based on practical experience. Similar Denso plugs look like new after 120k miles on my Landcruiser, That is why I decided to try them on a panther.