In addition to using an appropriate crimping tool, the material quality of ferrules is, says Phoenix Contact, crucial for optimum (and therefore reliable) connection. The hardness of the sleeve has a considerable influence on the workability and therefore the mechanical strength of a connection. The minimum hardness has always been defined in the standard by the specified tensile strength (Rm) of a min. 250N/mm ². However, inferior working results can also occur if copper sleeves are too hard, due to the poorer workability, and this can ultimately result in anything from contact problems to increased safety risks.