Read the stamp
Quadruple Plate silver marks
In Quadruple Plate silver marks, the phrase describes the manufacturer’s plating grade; it does not mean four parts silver or a 400 fineness.
Trade wording and item numbers
American plated hollowware can combine QUADRUPLE PLATE, a company name and a model number. The phrase describes the manufacturer’s plating grade; it does not mean four parts silver or a 400 fineness.
What to check next
Compare examples by the named maker to date the trademark. A design number on a teapot or sugar bowl may match a catalogue shape. STERLING and 925 belong to silver-alloy descriptions rather than these plating grades.