Abstract: Electronic temperature controller including a snap-on relay module which snaps into the electronic temperature controller. Any compatible relay module with any different numbers of poles can be accepted by manually disengaging a relay module from clips on the electronic temperature controller. Ball-stud assemblies on the relay module frictionally engage into a plurality of receptacles in the electronic temperature controller. A geometrical configuration provides for knob to potentiometer orientation and alignment including radial and axial stress relief for the potentiometer.