Federal law generally bans manufacturing switchblade knives for interstate commerce, or transporting and distributing them in interstate commerce. It also bans possessing switchblades in areas under federal jurisdiction. The law exempts the military, military contractors and common carriers.

But the law also exempts one other group, not defined by business or connection with the government, as to switchblades with a blade of three inches or less. A similar law in Maine was recently modified last year to exempt the same group.

What is that favored group?

Thanks to Dave Kopel, Clayton Cramer & Joseph Olson for letting me know about this, and thanks to the commenters whose comments on the magazine capacity limit thread reminded me of the puzzle. (I won’t go into more detail, so as not to offer too many clues.)

UPDATE: I originally omitted the “interstate commerce” qualifiers in the opening sentence; sorry about that.