Implantable medical devices include headers having various features such as a modular design whereby the header is constructed from a series of stacked contact modules. Additional features include a feedthrough where pins exiting a housing of the implantable medical device extend into the header to make direct electrical connection to electrical contacts present within the header where those electrical contacts directly engage electrical connectors of leads inserted into the header. Other features include electrical contacts that are relatively thin conductors on the order of 0.040 inches or less and may include radial protrusions where the radial protrusions establish contact with the electrical connectors of the lead. Furthermore, electrical contacts may be mounted within the header in a floating manner so that radial movement of the electrical contact may occur during lead insertion.