Knurling is usually similar to decorative or friction-increasing occasions, and the requirements for size are not too strict, such as 20.3 you mentioned above, and it may be 20.4 or 20.2 after knurling. If the drawings are not specially marked, you can communicate with customers for confirmation. Usually, the outside diameter before knurling is about: the diameter before knurling = the diameter after knurling -P/2. But this is not an accurate figure, because the final size is related to the shape of the knurling knife and the depth of knurling. The deeper the size, the smaller it is. The safest thing is to take a material head and let the lathe master test a shaft knurling with the same diameter according to specific materials to test a reasonable size. If the size is not strict, press -P/2 to round it off, and try to make it bigger. For example, you should press 19.7 or 19.8 for the above dimensions. If the knurling reaches 20.5, the outer diameter can also be ground.