Tariff-rate quota.

Two rates for the same goods, separated by quantity. US customs regulations define a tariff-rate quota as permitting a specified quantity of merchandise to be entered at a reduced duty rate during a specified period (19 CFR 132.1); once that quantity fills, the rest of the period pays the ordinary rate. Entries count from the moment of presentation, so a quota is a queue, and arriving after the fill is not something a broker can argue away. In apparel the same mechanism usually appears as a tariff preference level in a trade agreement, letting a capped quantity of otherwise non-qualifying garments claim the preferential rate, administered by CBP alongside the quotas (CBP). For a shop this is a supplier question rather than a customs one: a blank price quoted against an in-quota entry is not the same price once the level fills, and a supplier who cannot say which side of the line a shipment landed on has quoted a number that can still move after the shirts are printed.