A struck thru mint error occurs when a foreign object or substance comes between the obverse or reverse die and planchet (coin blank) at time of striking.

This Liberty Head $20 is the most dramatic struck thru that I have ever seen on a U.S. gold coin in over 45 years as a full time professional coin dealer specializing in mint errors. It is 75% struck thru, affecting most of the obverse design including the stars, crown, LIBERTY, and almost all of the hair detail.