Why are there ridges at edges of dimes and quarters?

Have you ever even stopped to think about why dimes and quarters (and fifty and one dollar coins) have ridges all around their edge? And, for that matter, why pennies and nickels do not?

It is actually both fascinating and obvious when you think about it.

First, pennies and nickels have always been made of inexpensive metal (hence the term "nickel" for a five cent piece). They have smooth edges.

Second, dimes and quarters were made largely of silver. They have ridged edges.

Why? Traditionally, whereever silver was used as coinage, there was a problem of people shaving metal off the edges of the coin, and thus devaluating the coin's worth. Hence, the invention of the ribbed coin which would show immediately any attempt at shaving.

The edges on our coins are a reminder that these coins origninally had a high silver content, even though they do not now.