The US "Anthony Dollar" coin is not particularly easy to distinguish from a quarter coin. The dollar has "flats" around the edge while the quarter has a round serrated edge, but the flats on the dollar aren't particularly obvious to sight or touch.
I have two of the dollars, received fairly recently as quarters in change, that I didn't notice until I tried to give one of them to an exceedingly honest cashier as a quarter, and she pointed out to me that I had a "real quarter" I might give her instead.
The US nickel (5-cent) and quarter (25-cent) coins are almost identical in weight and very close to the same size, although the nickel has a smooth rim rather than the serrated one on the quarter. Many years ago some of the guys in the lab discovered that a nickel placed between solid steel plates and "pressed" under approximately 17,000 pounds would expand sufficiently to replicate the slightly larger diameter of the quarter, and since the weights are almost identical the "squashed nickels" would be accepted as quarters by the soft drink machines. (The machines probably are more sophisticated now.(?))