Need bulkhead help

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When planning out my tank, found the outside thread of a bulkhead is made for the nut only, it's not the same as a threaded fitting (pipe thread (tapered?) vs standard).

Seems the connection to the bulkhead is to be internal only, either threaded or slip, not over the outside. The only exception I found where you would go over the outside was bard type bulkheads common in hydroponics.