Bill of materials
The list of every material, component and consumable a part or assembly needs, with quantities, that a quote and a build both hang their costs from.
On a single turned part the bill of materials is short, a bar, a coating, maybe a bag. On a weldment or an assembly it becomes the estimate’s skeleton, and the arguments start when 2 quotes carry 2 different skeletons. A missing hardware line, a bought component priced from a 2 year old email, fasteners counted per part when the print says per assembly, each is a bill of materials error, and every one is invisible in a review that only checks rates and cycles.
The quoting discipline is completeness with quantities, done during the takeoff rather than reconstructed afterward. Gross quantities, since the bar includes the cutoff and the sheet includes the skeleton left after nesting. Purchased items carried at dated prices with their minimum order quantities visible, because a $40 minimum on a 10 cent clip changes a small order’s price and a buyer will ask why. Consumables that scale with the work, weld wire, gas, abrasives, belong on the bill or in the rate, and the estimator has to know which convention the floor uses, because both at once is double counting and neither is a leak.
Where it costs money is revision traffic. The bill of materials is the document most likely to drift from the drawing, since a revision that swaps a component or a material grade can leave old lines priced on new prints. A quote that states its bill explicitly, line by line the way how to quote a machined part prices operations, is auditable against the revision in minutes, and the one that buried the materials in a lump sum gets to rebuild itself from the drawing every time the buyer moves.