How does stock get affected when an item is part of an assembly or kit?

Selling a Kit reduces each component’s stock proportionally. Building an Assembly reduces component stock and creates stock for the new finished item.

Kit Item - In a Kit, the stock of each component is reduced when the Kit is sold. For example, if a Kit contains 2 units of Item A and 3 units of Item B, selling one Kit will reduce the stock of Item A by 2 and Item B by 3.
Assembly Item - In an Assembly, when you build the finished item, the stock of each component is reduced based on the quantity used in the assembly. For example, if an Assembly requires 1 unit of Item A and 2 units of Item B to create 1 unit of the finished item, building one finished item will reduce the stock of Item A by 1 and Item B by 2.