Drawbar threads must be for something else. If memory serves they are locked in place with a cover which remains on the spindle. [ Just remembered, the cover locks open when you remove a tool. When you insert the next one it releases the cover which snaps shut locking the tool in the taper. ] Use a spanner to loosen the cover/cap. Their literature says the tool sockets are machined offset from center to accommodate the set screw pressure. Treasure them, set each one up with its own tool, Should lyou h ave CNC you can establish each tool's length and diameter and record it in the software.