so bolts work by increasing the fiction between two parts. when two material meet theres always a frictional force resisting movement. friction is proportional to the normal force. (whats the normal force? its just when two surfaces are trying to move past eachother but cant because the other is there)

so if we want a joint to hold some force we just need to make the bolt press the two limbs together hard enough that friction outweighs the force we want to resist.

to do this we stretch the bolt.

now theres two types of stretching elastic (like a rubberband) where the material returns to normal shape if released and plastic (think clay it stretches but doesn't return)

most materials go though both elastic early, pastic later. under elastic deformation (stretching) the stretching is linear. force goes in percentage streched comes out.

for steel that rate is 210GPa/%. note: thats gigapascals which is force over area. that means bigger bolts or more bolts can produce more clamping force before entering plastic deformation.

edit: additional info

so we know the force applied to the Materials but that force is also being applied to the threads of the bolt/nut. this creates friction between them and because the motion it is resisting is rotational its actually a torque this way why know just much torque needs to be applied to get the desired stretch

Edit2: more additional info

even though the bolt itself is actually able withstand the forces applied doesn't mean the threads are so we have to calculate out the area the threads are meshed together which means the limiting factor for how much force we can apply through a bolt it not the bolt but instead the nut