Tostão 'O-P' – João III 3rd type, Porto

João III's monetary reforms of the 1550s consolidated silver coinage under stricter fineness standards, and the Porto mint's output during this window was notably limited before operations there contracted further under Sebastião. The "O-P" mintmark distinguishes Porto-struck pieces from their Lisbon counterparts — a distinction that matters considerably given the relative scarcity of Porto production for this type.

Gomes 142 is among the less frequently encountered attributions in the João III silver series.