Existing computer tools for ergonomic design are unable to assist designers with higher level advice within design processes. Thus, design engineers need to rely on their own knowledge and experience when making crucial decisions relating to products’ ergonomic parameters. An intelligent decision support system has been developed in order to overcome this bottleneck. This paper presents a knowledge base, containing ergonomic design knowledge specific for hand tool design. A pneumatic hammer handle design is used as a case study in order to show how ergonomic design knowledge built within this system is used to improve the ergonomic value of a product. Relevance to industry Engineers in small and medium-size enterprises (SME's) or young designers are in an unenviable position as their knowledge domains and experiences are minimal. When applying decision support system discussed here, even SME's could appear on the market with optimal designed products with relatively minor influence on development budget. Consequently their role on the market will be aggrandised.