I inherited a load of tools from my father. Among them was this bit. I have never seen one like it, and don't know its purpose. It has six straight splines set at an angle to the long axis of the bit and sharpened to act as cutters. The diameter at the splines is 1/2" and at the smooth shaft slightly less than that. There is a hole in the tip that is 1/8" deep. The first half or so of the hole is conical, and the deepest part is cylindrical. I do not see or feel any threads in the hole. The following is stamped into the smooth part of the shaft: "National Detroit High Speed IVF [those three letters are slightly obscured from wear, but I think that's what they are] 1/2 [which must be the diameter]." It will cut into the edge of a piece of wood if put in a drill press with the wood pressed against the rotating bit, but the cutting is slow.
That is a straight reamer it's used to make a hole a precise size (drill slightly under-sized, ream to size, more precise than simply drilling to size.) The hole at the tip is used in making it and/or sharpening it (as made it will be exactly 1/2" - after re-sharpening it will be slightly less than 1/2")
It is NOT a router bit (and putting side loads on a drill press can have unfortunate consequences, so I suggest not trying to use it that way anymore)
Adding to Ecnerwal's answer, it's a 'straight-shank straight-flute' reamer, for making very accurate diameter (parallel sided) holes - but not in wood. It's for metal. Drill the original hole 10 - 15 thou (0.010 - 0.015") smaller than the finish, then ream to an accurate hole.
Being part of a machinists equipment, reamers are often not good to fit into a drill chuck, as they will have a Morse taper instead, which is designed to fit into higher end pedestal drills. This one doesn't have the Morse taper.