When my father-in-law died we came across this while cleaning out his shop. There are no markings on it. It measures 8" x 2.5" x 2.5" and is made of 1/4" steel tubing. The side bolts tighten flat jaws in the slot. The end bolt just screws in so it must be mounted to something with this end bolt? He had a wood lathe, drill press and radial arm saw. I've searched the internet for accessories for the tools he owned and and can't find anything similar. Can anyone identify what this is?