Difference between *product*, *material*, and *item*

Each of your definitions are fine. As you apply them to your particular circumstances,

material - the stuff the screws are made of, for example, titanium. Material usually refers to uncountable things. Even if the material is formed into countable units for sale (e.g., titanium bars), in itself it is usually a bulk item.

item - a countable thing, such as a single titanium screw. Item can also refer to a unit of an uncountable bulk material. Three packages of polishing compound might be called three items. But units that are not separately packaged (handled by amount) generally would not usually be referred to as units. Three pounds of titanium would not usually be called three items.

products - refers to anything that is produced. This can include countable and uncountable things. Titanium screws are products. Refined titanium itself is a product (it is processed to get to that state). But materials in their original state, unprocessed, are not products. Water in a stream is not a product, but filtered, bottled water may be considered a product.

Your implant screws are products and items, but not materials.

Nice answer from "bib", and I agree in the context of Manufacturing.

In Sales, a different set of definitions may be more appropriate:

Product - something you sell or deliver to a customer e.g. A Tin of Beans

Material - something you buy or assemble to make the Product e.g. Tin of Beans consists of Tin, Label and Foodstuff. Foodstuff consists of Beans , Tomato, Water, Salt. Materials can be purchased but cannot be sold, but may have a 1:1 relationship to a Product

Item - a specific instance

The reason for the difference is reselling. You may buy a Material and immediately resell it as a Product. Counter-intuitively the same physical item is actually 2 different things here as Product and Material are Roles being played by the item. Most IT systems have these 2 separate concepts with the ability to link them 1:1.

Note:

A Product may be a Service - i.e. a Product where there may be limited or no physical item involved.

A Material may also be a Resource such as equipment used to machine an Item, or Staff who perform the work. The customer doesn't receive the Resource, but it is used during the product creation.