boltsscrews
Why do lag screws have the unthreaded body between the head and the threads?
And why is that 'Body' the same diameter as the outer 'Thread' diameter?
Why doesn't the transition immediately abut the head, letting the threads run down a greater portion of the bolt?
You may not use electro-galvanized bolts for ledger or joist-beam attachments.
See IRC 502.2.2.1. Hot dipped or stainless steel only.
Electro-plated is also not appropriate for contact with treated lumber.
It may be that the bolts you listed are hot-dipped, but usually those magic words are listed, due to the code requirements.
You are not going to find this on a shelf, you may get one from the manufacturer of the chair, if you talk nice and beg. Otherwise the chance is slim.
I would get a pan or philister head machine screw with the threaded portion about 1" longer than the screw pictured is over all. Chuck 3/4" of the threaded end in a drill and crank it down. Turn on the drill, keep it steady and run a file to grind off the threads exposed beyond the drill chuck to smooth the shank like the one in the picture. Since the screw is longer than needed and the drill damaged the end of the threads to hold it while it was spinning, cut it off and soften the corners like the original.
The drawing I referred to earlier
Best Answer
In many cases an unthreaded shank provides a better, more secure fit when mating to the components that it connects. Where lateral movement is a concern, this type of bolt should be used.
In other cases, it's important that there be no pull on the upper portion of the material being joined. Threads would create drag that may counter the bolt's ability to bring two parts together with force.
There are two reasons that the unthreaded portion has the same diameter as the threaded portion. The first relates to what I mentioned earlier--a close-tolerance fit to the other parts of the system. If the threads were raised with respect to the shank (and some bolts are like this for various reasons), the bolt would be sloppy in the bore after insertion.
The other is more mundane--it's easier from a manufacturing standpoint. Threading machines typically remove material by cutting. This obviously leaves threads that have inner diameters smaller than the bolt's shank.