Print in ABS for best fit. For PLA you might need to adjust the center whole with a tool.Pry the knob from the Ultimaker2 by using 2 tools, one on each side. You need only the knob not the light ring around it!Attach the new knob. Don't use a lot of force. If it doesn't fit use a tool to widen the center whole a bit.Edit: Changed the design of the center whole a bit. It should be a snugly fit even with building tolerances.