Yes, you can put a bolt in a catalytic converter to help prevent theft. They’re easy to install with a ¼-inch flathead screwdriver but impossible to remove unless you have a special security pin.
Bolts are also typically tamper-resistant, so no matter how hard potential thieves yanks and pull, your catalytic converter will remain snugly fastened to the underside of your vehicle.
To use them, you simply need to replace the bolts that fasten your catalytic converter to the undercarriage of your vehicle with special security bolts.