This is likely your pim drive nut replacement =>
Pin Drive Lug Nuts
Part of the confusion is from mixing the metric and imperial measurement systems, and part is from sloppy measuring techniques.
Your 19.01mm diameter is measured partially off the top edge of your caliper's flat measuring surfaces. Remeasure correctly on the flat and parallel machined measuring surfaces of the caliper jaws. The number you get will be larger and very likely the 0.770" Imperial measurement or the 19.5mm metric equivalent on the web page above.
Be sure to match the chamfer angle your pin drive nuts use. You can not mix angles without doing damage. Yours will be either 45˚ or 60˚.
You will also need to properly identify the thread diameter and pitch your wheels use. The Vintage site will require selecting one of five different wheel stud diameters and thread pitches.
Attention to detail will be your friend until you get the stud nuts properly ID'd. Actually, it will be your friend long after that also ...