Specifically, if a flanged duct fitting (7307.19.3070) has a bespoke modification so that it can be attached to a specific flow meter (heading 9026.10.2040) would it still fall under the general use definition set by sec. XV note 2 thus disqualifying it from Ch. 90? Per GRI note 3a 7307 is the best heading for this as it describes exactly what it is but how much modification is allowed to take place before it can no longer be considered for 'general use' and could instead be placed into ch. 90 as a 'part of' a machine? – Sam D May 15 at 20:32