Edge vs. Rim
Ever since the Presidential Dollars have come out, many people seem to have a hard time distinguishing between the rim of the coin, and the edge. These terms have very specific meanings; make sure that you are using them correctly.
The Edge of a Coin
The edge of a coin is sometimes called the "third side." Experts call the heads side the obverse, and the tails side the reverse, reserving the term edge for the third side, or the side that you see if you look at the coin in the space between the obverse and reverse.
The edge runs around the entire circumference of the coin, and is the portion that has the reeding on it if it's a dime or quarter dollar. The edge is plain on pennies and nickels.
The Rim of a Coin
The rim of a coin can be found on either side. In fact, a coin can be said to have two rims, one on the obverse and one on the reverse. The rim is the up-raised flat part of the coin that completely encircles the diameter on both front and back. On U.S. coins, the rim is usually very thin, but on Presidential Dollars it is much wider, the purpose being to allow blind people to tell the dollar apart from the quarter dollar coin by touch alone. (This standard was created back when the Susan B. Anthony dollar also had the reeded edge, so the lack of reeding wasn't enough for the blind to make the distinction.)
Originally the rim of the coin was solely imparted during the striking process. When the coin die was produced, a recessed flat area that encircled the design elements on the die was imparted at the very end of the die production process.
When the die was used to strike a coin it left a raised flat rim around the circumference of the coin.
As coin production processes evolved over time, the addition of a collar inside the coining press is used to hold the planchet during the striking process. Before coins are sent to the coining press, they are passed through an "upsetting mill." The upsetting mill contains a rotating wheel within a channel that slightly get smaller in order to squeeze the coin slightly.
This imparts a small raised rim on each side of the coin. Additionally, this results a uniform diameter on each and every coin that goes through the upsetting mill.
When the coin is ready to be struck it falls into the collar that holds the planchet between the two dies for striking. Additionally, this raised rim that is imparted before striking helps the metal flow consistently into the recesses of the coining die in order to aid in the striking process.
I have shown these two important parts of a coin in the photos with this article, or you can see what all of the parts of a coin are called.
Edited by: James Bucki