14mm, 0.33 grams.

Interesting piece - it is a half of a severely clipped penny of Henry III, probably intended to be a farthing (since it is of the correct weight for a farthing, not a halfpenny). Interesting and unusual.

Old English pennies were cut into halves and quarters to create smaller change, as there were no readily available smaller denominations like halfpennies or farthings until King Edward I introduced them in 1279. People would cut a penny in half or into fourths to make smaller transactions when needed.