Just to make things clear: the only blades allowed are here:

http://www.tsa.gov/interweb/assetlibrary/Permitted_Prohibited_12_18_2003.pdf

Any other blades are prohibited on board. A tape covered blade is easily confirms the hidden weapon badge and leans toward a more complete search (delays included) and possibly legal prosecution.

(For my disclaimer, I'm not a fan of the present regulations, but don't want anyone to spend his/her holiday season in a terminal, or even worst places.)