Custom manufacturers of chemicals, also called tollers, make use of general-purpose equipment to meet chemical manufacturing needs of their customers. They are often called upon during the development stage of a product cycle, when less than full-scale production is required for demonstration purposes. However, the arrangement may also be longer or indefinite, when a toller has production capabilities that its customer does not have and wishes to permanently outsource. Many chemical companies engage in some custom manufacturing activities as part of their business model. Only companies for which this is a primary activity are listed in this category.