Reeds are what give a coin the grooves (or ridges) along the edges. The reeds are an anti-counterfeiting measure and to make sure coins have not been intentionally filed down.
When coins were made primarily of gold and silver, people would file off the edges of the coin to get some of the precious metals. Reeds were developed to make it immediately obvious if a coin was tampered with.
How do reeded edges prevent counterfeiting?
Anything that makes a coin more intricate is helpful to prevent counterfeiting. By making a counterfeiting job more time consuming and requiring it to have more special tools, the barrier to entry of counterfeiting becomes much harder.
Although no one will stop to count the reeds on a common dime, if a coin worth hundreds is being graded, the graders will check the reeding.
Why don’t pennies have reeded edges?
Since pennies have always been made of copper and zinc, there was no fear of the coins being filed down for their copper content.
Even though pre-1982 copper pennies are worth about 2 cents in copper today, you could not file enough of a penny to make a profit and keep the coin recognizable.
How many reeds are on each coin?
The number of reeds is available on the US Mint Website. The three coins in circulation with reeded edges are the dime, quarter, and half dollar.
Number of Reeds:
Common Circulating Coins:
- Dime: 118
- Quarter: 119
- Half Dollar: 150
Uncommon Coins:
- Morgan Dollar: ~189 (Rare Variety: 154!)
- Peace Dollar/Eisenhower Dollar: 189
- American Silver Eagle Bullion: 201
- Susan B. Anthony Dollar: 133
Reed Errors
Some coins have been found with more or less reeding than they were intended to have. This is almost always due to a machine error.
One recent coin to be found with a reed error is the New Mexico 2008P Quarter. There is a very good article about it on error-ref.com. Along with this image:

Even most coin collectors neglect to look at the reeding of coins. This is probably why these errors are so uncommon. Most people do not notice if a coin has 189 or 154 reeds (like in the case of the Morgan Silver Dollar).
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