Not sure. Texas penal code 46.02 prohibits the carrying of prohibited weapons unless in your own premises or en-route to your own vehicle or watercraft. You can own them, make them, sell them apparently, but can't carry em. 46.01(6) defines an illegal knife as a blade over 5 1/2 inches, something designed to cut or stab by being thrown, a dagger, a bowie knife, a sword, and a spear amongst other things.
It seems to be called out by name specifically, no idea why. May have something to do with being pointy, or having two edges sharp?
A switchblade knife however, that does not meet definitions of other prohibited weapons, is a-ok it seems.
YinTx