There is disclosed a modular prosthetic conduit system such as a stent or stent graft system tailored for the repair of aneurysms or other compromised vessel walls. The stent or stent graft system incorporates various means to interlock the multiple modular components used in the repair procedure. There is further provided a modular stent graft system tailored for the repair of aneurysms or other compromised vessel walls that cross or are adjacent to a branch or bifurcation in a vessel.