• Each element in a drawing is given a reference number.• Identical parts shown in the same assembly should have the same item designation.• The item reference is a number that is added as a serial feature to objects that are listed in parts lists and listed ondrawings. The reference number must be sorted in ascending order.• According to ISO 6433 alpha- numerical Item references -especially for the electro-mechanical purposes- are permitted.• If a revision results in an item having to be removed from a BOM, the remaining items retain their numbers, reducing theneed to revise the drawing and other associated documentation.• The field "Item number" may be left blank in the parts list section for a single part.• For appropriate drawings and other documents indicated immediately below the item, the item number remains blank.