NNP

Center Hole.  Round aperture in exact center of a numismatic or medallic piece. If it is formed with a rotating drill it is called a drill hole, otherwise it is made with a piercing tool before or after blanking. It is the most common form of openwork. With the rise in bimetalic technology for coins and tokens it is becoming more important as the ring blank has a large center hole for insertion of the plug blank before striking.

excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators

COMPILED AND WRITTEN BY D. WAYNE JOHNSON

Roger W. Burdette, Editor