The tiny pocket found in most pairs of jeans has been a mystery to most of us.
It's too small to fit anything of use in today's world but is still part of many jeans you buy today.
But it did have a very important use back over 100 years ago.
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The reason behind those small pockets dates back all the way to 1890.
Back then these small pockets were stitched into pairs of Levi waist overall' jeans as a place to put your pocket watch.
Tacey Panek, Levi Strauss & Co's historian, told Insider: "The oldest pair of waist overalls in the Levi Strauss & Co. Archives (from 1879) includes the watch pocket.
"Our 19th century overalls had a single back pocket on right side of the pant beneath the leather patch."
The tiny pocket is apparently never found on suit trousers because a pocket watch would be part of the inside of a jacket for formal wear.
Seeing as not many people use pocket watches these days, it may seem a bit pointless they're still there.
However, it's actually due to sentiment with regards to WWII, as to why they are still around.
Panek explained: "One interesting fact about the watch pocket is that during WWII the two corner rivets were removed as a way to conserve metal for the war effort."
"The rivets returned to the watch pocket after the war.
"It was riveted in the top two corners and included our recognisable arch design, called the Arcuate, stitched with a single needle sewing machine."
"The watch pocket was an original element of our blue jeans, like the rivets on our pockets, button fly, arched back pocket stitching and leather patch.
"To preserve the integrity of the early design, Levi Strauss & Co. maintains the watch pocket."
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