Vacuum diffusion bonding is a process whereby separate parts are joined without the use of filler metal. Vacuum diffusion bonding relies on temperature, pressure, time, and a very clean atmosphere (vacuum) to create the bond. Typically parts are small and able to be placed between two specialized plates that are held together with threaded rods. These threaded rods are made from materials that do not expand as much as the subject materials when heated, creating the extreme pressure required to make a solid bond.