Here's the list - for teaspoons only. These specs are supposedly well established in the industry. I don't know whether they are stamped, as such, or not. I also don't know the numbers for other types of pieces.
Half plate - 1 tr oz Ag/ gross (144 pieces) of teaspoons
Standard plate - 2 tr oz/gross
Double plate - 4 tr oz/gross
Triple plate - 6 tr oz/gross
Quadruple plate - 8 tr oz/gross
Federal specification - 9 tr oz/gross
The silver thicknesses, on these, range from .000150" to .001250". The Fed. spec. ones figure out to 1 tr oz/sq.ft. of surface area.
Here are similar plating standards for plated hotel holloware. A dwt. (pennyweight) is 1.555 grams. There are 20 dwts in a tr oz.
Light plate - 2 dwt/sq ft
Medium plate - 5 dwt/sq ft
Heavy hotel plate - 10 dwt/sq ft
Extra heavy hotel plate - 15 dwt/sq ft
Federal specification plate - 20 dwt/sq ft