An improved ultrasonic transducer for measuring stretch loads on bolts is provided. The improved ultrasonic transducer is separated into a pickup unit and a base sensor unit. The base sensor unit includes a piezo ceramic inside an aluminum can covered by a PCB for protection, which is surrounded by a strong magnet. Honey is used as a couplant between the base sensor unit and the bolt during operation. The base sensor unit stays on the bolt before and after tightening without changing the mechanical bonding between the sensor and bolt therefore achieving higher accuracy stretch readings. The base sensor unit is low cost and reusable, as it can be placed on number of bolts before tightening and can be removed after tightening, washed and then reused.