A foldover strike occurs when a planchet or coin is struck on edge and folds from the impact. Any number of scenarios can produce this rare vertical positioning of the planchet.
It can enter the striking chamber spinning or rolling on its edge. It can be kicked into a vertical position when thrust against a coin left behind in the striking chamber. An airborne planchet can even be caught in midflight by the descending hammer die.
The most recent foldover strikes I know of are dated 2001, so this seems to be an obsolete error type that modern high-speed Schuler presses used at United States Mint facilities are incapable of generating.
Appearance highly variable
As might be expected of such a fluke event, the appearance of a foldover strike is highly variable. Variability includes the distance of the bend from the planchet’s equator, the positioning of the struck tongue along the convex edge of the “taco,” the size of the tongue, and the relative contributions of the tongue’s two fused flaps.
Also variable is the presence, size, and patency of any “loop” that forms as the two halves of the taco are pinched together.
Appearance is, in turn, dependent on thoroughly random starting conditions. These include the planchet’s contact point on the anvil die face and whether the bend is directed toward or away from the striking chamber.
Also important is the planchet’s angular orientation to the circular die face (tangential, oblique, or orthogonal). Stated another way, the silhouette of a peripherally placed planchet would respectively appear as a circle, an oval, or a vertical line when viewed from across the striking chamber. Frequent slippage of the planchet during the downstroke of the hammer adds an additional level of complexity.
2001 Lincoln cent struck twice
Our first example is a 2001 Lincoln cent that received a normal first strike and a foldover second strike. It’s evident that the vertically positioned coin was peripherally located because the second letter of WE is preserved on the edge next to the tongue. The bend pointed away from the striking chamber (producing a patent loop) and is perfectly symmetrical (an axial or midline fold).
On the composite tongue, the obverse flap is fractionally smaller than the reverse flap. The tongue is asymmetrically positioned along the convex edge of the taco.
Some consistent patterns
This example does document some consistent patterns that can be detected in double- and triple-struck foldover cents. In such errors, the outside of the fold always shows the Lincoln Memorial.