I have no idea what the actual knife laws are in Mexico, but when I go to places like Mexico, I worry less about the law than I do about venal law enforcement personnel. In other words, regardless of what the law actually stipulates, you run the risk of having any knife confiscated by any official who takes a fancy to it. Or, if the knife has little intrinsic value, perhaps the cop will use it as a pretext to hassle you for a bribe.
Most tourists don't know much about what's legal and what's illegal in foreign countries. If a cop says your knife is illegal, what are you going to do? Call a lawyer? Go to a library and look it up? How good is your Spanish? How much of your vacation time do you want to spend settling a dispute? For most tourists, the hassle or fear of unknown legal consequences, not to mention the language barrier, puts them at a real disadvantage when arguing with policemen, customs officials, etc., so my advice is to plan on surrendering the knife if it comes to the attention of a cop.
The next time I go to Mexico, I plan to take nothing I can't afford to lose--probably an Endura. I will keep this knife out of sight except in cases of dire need. I'll also have a spare in my luggage in case I have to give away the one I'm carrying. I will also have something smaller and innocent looking, such as a Swiss Army knife, to actually use in front of people.
David Rock
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AKTI Member # A000846
"Never carry a knife shorter than your schnoz."