The lead into a choke tube does need to be slightly larger than the parent bore.Otherwise the ejecta (shot, wads, propellant) can get behind the choke sleeve if there was a step, which in turn could cause catastrophic damage.Adhesive, solder, threaded or interference (sweated) fit will all be sufficient if the job is engineered correctly.But specific shell loads or jug choking (assuming sufficient material in the tube) may be a more cautious choice.