Also known as a "knuckle knife," the blade "folds into the handle of the knuckles," Transportation Security Administration Spokesperson Lisa Farbstein said.
The double-edged trench knife was invented for close-quarters combat during World War II, when fighting predominately happened in trenches. The "knuckle-duster" handle was intended to protect the fingers and provide a secure grip, but it also added to force to a blow.
Knives, like guns, are prohibited on planes.
"And brass knuckles are illegal in NYC," Farbstein noted.
The weapon and the traveler were turned over to Port Authority Police.
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