Capto C5 PSC5 PSK50 Blank Modular Connection Shank Tool Holder Blank
Blank C5 Tool Holder, Previous owner had milled a 0.75" / 3/4" Channel looks like to hold a stick Turning tool in it.
3.964" Over All Diameter on the Tool Holder Blank
Height is roughly: 5.0", not counting the connection point. so you have roughly 5.0" of 3.964" Diameter steel to work with minus what has been cutaway for an OD turning tool.
JC