Dear All,
Thank you again for your comments. Today I had a chance to do some measurements:
1) Valve stem: D 0,625-0,630 inches or 15,81-16,06 mm;
2) Bigger side of the shaft on the lower end of the pushrod (or pull rod): 0,593-0,596 inches or 15,07-15,15 mm;
3) Stainless steel sheet on the upper part has a thickness of 1 mm;
4) Height of the valve seating is 10 mm.
Please note, that the measurements were done with a caliper capable for both mm and inches.
According to the above I would say it is closer to be metric than a US Standard.