First, please check the shaft of your torque detector. If the shaft is yellowed, it is painted the rust prevention.
For the SS series, DD series, and DSTP series torque detectors, the rust prevention (yellow) is applied with the shaft of them when they are shipped without coupling.
For the MD series torque detectors, the rust prevention is not used even when they are shipped without coupling. But the rust prevention is applied depending on the situation when the MD series is shipped installed to the MT series.
When you install the coupling to the shaft, please remove the rust prevention before installation. The rust prevention can be easily removed with thinner.