Unsharp Mask

What is the correct setting in usm for RADIUS and THRESHOLD

There is no one correct setting. It very much depends on the image and the reproduction size. Without knowing what size and the output device, its hard to even give you starting points. If your question is about web posting, I use the following:

For images taken with the EOS 10D, I find the following to work very well - apply all three below:
150, 0.3, 2
100, 0.2, 2
100, 0.2, 2

Hi Jack---Sharpening is actually placing a halo around the areas of contrast. The amount is the intensity, the radius tells you how wide the halo is, and the threshold affects noise. In an image with lots of detail such as trees, grasses, feathers, and fur, the radius will be .2 to 1.0 depending on the file size. The smaller the file (such as we post at Naturescapes), the smaller the radius. A smooth image with less detail looks best with a radius os 2-3 pixels. A pumpkin is often given as an example of a smooth image in this category. E.J.'s formula works well, but also 100, 0.2, 0 repeated a couple times works very well. If posting a sharp bird image, you might also do the above, then select just the eye and give it one more click. That is one way to bring out the highlight when one is present, but very faint.