When viewing a product page the quantity in the table next to the add to basket button is the minimum that can be ordered.
In the case of screws and other such fixings, these may show a quantity of e.g. 100 or 200. This is how many are supplied in a single box and ordering multiples will result in full boxes, for example if the quantity is 200 and 1,000 are ordered, five full boxes of screws will be delivered.
If full cartons are required, the carton quantity which may be displayed on the product page in the table needs to be ordered, for example if the quantity is 200 and carton quantity is 18,000, two full cartons will be delivered, which would make a total of 180 boxes of screws.