A milling tool holder having a spindle with a tapered opening and a tool holder having a tapered shank that fits into the spindle opening. The narrow end of the shank has a split collar. The spindle is joined to the tool holder by inserting the shank into the tapered opening and drawing the two components together using a differential screw. When the differential screw is turned in one direction, the two components are drawn together, and when turned in the opposite direction, the two components are separated. As the shank bottoms in the tapered opening, an annular enlargement on the differential screw expands the split collar of the shank to tightly seat the shank in the spindle.