External but they do thread in before and after the cat.
Keep in mind that a catalytic converter has an 8 year or 80,000 mile warranty by Federal law. If it needs replaced due to failure you could have it done for free if it's within the parameters. If you are out of that, then most exhaust shops can install an after market universal cat if it's not a warm-up type for around $150-200... If it is a warm up places like smith brothers online can sell you a re manufactured unit.
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