Jim,
I lightened up and focused your pic and saw the flat sides on the screw heads.
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It also looks to me like the unthreaded part is an eccentric. If that's the case I'd say they are a screw for some of the rods under the bed of a machine.
Now, about that ruler marked off in 10ths. I want one. Hopefully it's metal. Where do you get them?
Joe