The TSA is seeing big increase in the number of people trying to get a certain kind of knife onto flights in the U.S.

They're called credit card knives.

"These are the size of a credit card, hence the name, and they are plastic, except in the middle where the blade to the knife is metal," Lorie Dankers with the Transportation Security Administration said. 

Dankers says almost 530 credit card knives have been confiscated at 68 different airports this year, and 30 were confiscated in San Francisco.  

In contrast, the TSA agents have not found any of these credit card knives at Sacramento International.

Dankers believes the knives are showing up more often simply because they're more commonplace these days and easily forgotten as a pocket item.