On two of my cars (over the years i’m not rich) i’ve noticed that the strut was held on by a one bolt compression fitting . How, with all the weight and stresses a wheel encounters while driving, does this not break or come apart? I’ve really always wanted to know this.

If you are talking about the upper mount, the threaded rod goes through a fairly good sized bearing that rotates as the wheel is turned. Also the weight is on the spring underneath, not on the threaded rod. The rod is just the torsion part of the with the weight on the spring and bearing plate secured with three bolts. Just take a look at the diagram. The bearings will wear but that’s about it.

Are you referring to the nut that holds the upper spring pad and mount in place and keeps the spring compressed?
If so, the shear strength of the threads is strong enough to keep the spring compressed. As to not coming apart while driving, that does not happen because the upper strut mount is compressed against the body of the car (strut tower) and that is absorbing the stress rather than the threaded shaft and nut on the strut.

Bushings. They absorb shock.

And many materials that can absorb shock, as well as many that don’t (such as steel) have considerable compression strength before failure. Take the tread blocks on your tires, for example.

Materials have strengths of different types. Compression strength, tensile strength, and sheer strength. Some materials such as granite and unreinforced concrete have phenominal compression strength but poor tensile strength. Try to put a granite or unreinforced concrete beam horizontally between two posts far apart and the lower half (which is under tensile load) will fracture and the beam will fail. Yet a granite slab will hold up a skyscraper if the support underneath it is even and stable.

Besides, your tire absorbs a great deal of the shocks and stresses of driving.

The only think attached to this bolt is the piston rod of the struts shock absorber. The top of the spring goes to a large rubber block called the upper strut mount. Its held in place with three or four bolts.