The shim washers are placed on the male M27 thread of a DMT blade when it is connected to a seismic module with Prolub. The washers are used to enforce the vertical misalignment between the shoulders of the DMT blade and the sensors on the seismic module. The misalignment prevents the DMT from removing – during penetration – the soil that provides the required contact between the sensors and the soil transmitting the wave.

Important Note: Incorrect misalignment betwenn DMT shoulder and seismic sensors causes to record unclear seismic traces, with the difficulty or impossibility of determining a wave velocity.