Both screws are fixed. In this way, the fixed bearing can bear the axial force at the same time, and the proper pretightening force can be applied to the screw to improve the supporting stiffness of the screw, and at the same time, the thermal deformation of the screw can be partly compensated. Therefore, large machine tools, heavy machine tools and high-precision boring and milling machines are mostly using this structure. Of course, there are also shortcomings, that is, the use of this structure will make the adjustment work more tedious. 

In addition, if the pre-tightening force of the two screws is too large at the time of installation and adjustment, the final stroke of the screw will be longer than the design stroke, and the pitch will be larger than the design pitch; and if the pre-tightening force of the two nuts is not enough, it will lead to the final stroke of the screw longer than the design stroke and the pitch will be larger; and if the pretightening force of the two nuts is not enough In that case, it will lead to the opposite result, which can easily cause the vibration of the machine tool and reduce the accuracy. Therefore, if two fixed structures are adopted, it is necessary to adjust them strictly according to the instructions, or with the help of instruments (dual-frequency laser measuring instruments), so as not to cause unnecessary losses.