The 1876 Z1-AB variety comes from the Engraver family with 3 other varieties. This variety was struck on a brass planchet and silver plated. Either die details or striking rarely produced well-detailed examples of any varieties from this family. Also, this counterfeiter produced some of the crudest hand-made, die struck counterfeit Seated dimes between all other families.
 
This is a higher-grade example of this variety with about 50-75% of the silver plating still present on the surfaces.  Fewer than 5 examples of 1876 Z1-AB have been documented to-date.
 
I also have another example from this family available to purchase, 1880 Z1-AF, making this a very rare opportunity to build a collection of varieties from this family.