Torq-Tenders from Zero-Max Inc., Plymouth, Minn., are positive-drive couplings that provide accurate overload protection in mechanical power-transmission systems. When load exceeds the rating determined by precision-tempered torque springs, the unit's drive key pivots out a slot to disengage the coupling. Once the over-load is removed and the speed reduced, the unit resets automatically, engaging the drive shaft and putting the drive system back into motion at original position. Custom models and sizes are available. The smallest unit is TT1X with a 2 to 60-lb-in. torque rating and TT4X is the largest with a 750 to 3,000-lb-in. rating.