This paper highlights various types of pre-existing parts in SolidWorks and CATIA referring to the possibility of creating new customized parts or blocks. These parts were intended to help those who work in this field and increase the efficiency of designing. For example, they are used in assemblies with bolts, screws, nuts and washers modeled in SolidWorks and CATIA. These software use special tools to add rapidly fasteners to the available holes features in assemblies. The work also presents the possibility of accessing existing parts libraries created by the users or specialized companies and posted on the Internet. In order to illustrate this activity with standardized components, flexible couplings are used.