These convenient devices STT R100 NO and STT R150 N are especially suitable for the application directly in the production environment. By placing the STT on the surface of the test object existent twist structures are immediately visible. When the shaft is fixed on a V-block or between rotatable centers, by rotating the shaft, local dependency of the sealing surface structure can be easily and quickly tested. The device STT R100 NO is designed for shaft diameters from 5 mm to 200 mm. The device STT R150 N enables to test shaft diameters up to 300 mm. Due to the compact and robust aluminum housing and the battery powered laser the device is ready for operation even under harsh production conditions. Additionally, the device STT R100 NO provides the possibility to connect a tripod (1/4” 20 UNC).