When the two parts are mated together, these projections are the high points that first make contact. As the power is cycled, the projections simultaneously carry the current and are welded. Due to the efficiency of power transfer, thicker materials can be successfully welded. For thin stock, the traditional spot welding is a preferred method. Low carbon steels, low alloy steels, stainless steels, as well as aluminum can be welded using this process.
Projections are usually semi-spherical or blunt conical type.