Then they should be merged into a compound or connected with tie constraints.
https://calculix.discourse.group/t/how-to-consider-pretension-in-spring-elements/1716
Actually, the best way to model preloaded bolts with CalculiX is via simplified solid models (basic cylinders) discussed in several previous threads such as: COMPRESSION ONLY for simulating bolts and nut faces - #12 by fatmac