Expect to need to clean up the milling work or have your tolerances slightly off. If you will later want multiple matching hotends, buy them all at the same time. Drill bits for nozzle sizes can be found at Harbor Freight if you are in the USA. Using the cutting side of the bits very carefully and then using the dull side for polishing seems to work. Some guy uses toothpaste to help with the smoothing of the finish. You may find the knockoff hotends to have a different diameter of cooling fins orother parts of different sizes than what you were expecting.