I recently acquired this coin as the Corinthian helmet appealed to me and it was inexpensive. Can anyone add any more information ? ASIA MINOR. Uncertain. Hemiobol (5th century BC). Obv: Facing Corinthian helmet. Rev: Quadripartite incuse square. Weight: 0.33 g. Diameter: 6 mm. Here are 2 similar (but not identical) ones I looked up, also sold as unknown hemi-obols from Asia Minor Numismatik Naumann 43, lot 296 Euro 80 Triton XII, Lot: 355. $850 (!)
Several similar types on sixbid: Use this search string: helmet *obol* incuse corinth* https://www.sixbid-coin-archive.com/#/en/search?text=helmet *obol* incuse corinth*¤cy=eur
I know little to nothing about the coin, but if I'm unsure about the coin type (i.e. obole, hemi-obole, or whatever type), it helps to add a wildcard (asterix) before and after the coin type (i.e. *obol*) which will then yield all types of strings that have 'obol' in it.