U.S. coins and ridges

Every time I reach into my piggy bank and grab a handful of coins I seem to notice that many of them contain ridges. I hadn't really thought much about it until recently when I decided to figure out the meaning of the tiny groves. Upon doing some research I discovered a page on the U.S. Mint's website dedicated to my exact question.

Basically, the "reeded edges" as the mint puts it, were originally put in place to "deter counterfeiting and the fraudulent use of the coins, such as filing down the edges in an attempt to recover the precious metals." However, despite the Mint's stoppage of using precious metals in our coins they have continued the use of reeded edges for the visually impaired. As the Mint puts it: "...the ten-cent and one-cent coins are similar in size; the reeding of the ten-cent coin makes it easily identifiable by touch."

This makes me wonder what kind of other tricks and quirks some of our most common items have in place that most of us just aren't aware of.