The bargaining leverage of suppliers is stronger when suppliers provide an item that accounts for a sizable fraction of the costs of the industry's product. the products of suppliers are weakly differentiated and the supplier industry is composed of more than five suppliers. industry members are a threat to integrate backward into the business of suppliers and to self-manufacture their own requirements. there are no good substitutes for the items being furnished by the suppliers and when there are only a few "preferred" suppliers of a particular input. industry members purchase in large quantities and thus are important customers of the suppliers