Fiddle Coins, unlike worry coins, have a bearing on the reverse side which allows them to spin for 14-17 minutes on smooth surfaces. They are most often 1.5" diameter and have been made with a wide variety of natural and man-made center sections.
Solid Fiddle Coins
Fiddle Coins with metal centers are commonly made in 1.25" as well as 1.5" diameters.
Non-spinning versions of the Fiddle Coin, worry coins have no bearing and can be flat or convex on the reverse side. They are generally 1.5" diameter.
Mokume Gane Worry Coin
1.3" mokume gane worry coin. Etched on the sides and reverse.