An unusual circa 1870 4-jaw self-centering drill chuck of about 3/8 capacity and most unusual construction: the No.1 Morse taper shank - machined with a keyway along its parallel section - is screwed, using what appears to be an Acme thread, into the inner body of the chuck. Inside the chuck a pin engages a hole through the end of the thread - but apparently missing is a knurled knob of some kind that would have been secured to the shank and used the keyway to tighten the jaws