Single frequency, variable frequency and simultaneous dual frequency technologies are now available for the heat treatment of gears. Single frequency hardening for high volume dedicated applications allows for manual tuning, while variable frequency allows for tuning with the push of a button. This technology matches frequency to a diametrical pitch. The simultaneous dual frequency (SDF) process is easily integrated into new or existing manufacturing lines or as a flexible workcell. Shorter heating cycles can be accomplished using an optimal frequency mix of medium and high frequencies combined with high-power output, reducing distortion. Because overall heating associated with SDF is reduced, the microstructure of the hardened area is improved with minimal effect on material core properties. SDF can eliminate the need for final machining as dimensional specifications are unaffected after hardening.