It must be ensured that the medium flows against the sensor of the thermometer. This generally occurs when the thermowell tip is located in the middle third of the pipe. The insertion length of a thermowell or protection tube depends on the thermometer used. For mechanical thermometers, a minimum insertion length of 60 ... 100 mm is assumed, whereas electrical thermometers only require an installation length of at least 35 ... 50 mm. The maximum insertion length for protection tubes is limited by the manufacturing length of the tubes (approx. 5 to 6 metres) and for thermowells by the manufacturing length of the gun drill machine (between 1,000 and 2,000 millimetres, depending on the model). However, longer thermowells can also be produced by welding individual pieces together.