What type of tool or bit is a metal shaft with splines?
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&quot; - after re-sharpening it will be slightly less than 1/2&quot;)
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)