I'm going to go out on a limb and assume that this is a replica of a Massachusetts 3 pence colonial coin. The well rounded planchet (with no signs of tooling for weight adjustment) and even strike argue strongly against it being authentic. But, I found this in a dealer's junk bin and would love a second opinion before I consign in to the "not paying for my next round the world trip" drawer. After all, these do occasionally turn up in unexpected places: http://lunaticg.blogspot.com/2014/09/1652-new-england-3-pence-coin-found-by.html
Don't buy your ticket, definitely a cast replica. It is a poor copy of an Oak tree threepence. A genuine coin would be paper thin, and not have the rough cast look, plus as you mentioned the round planchet and strong images.
