The serration cutter is just a ground down tap. In this case, I have several 5/16"-32 taps. They are two flute, I ground one flute smooth and about 1/2 of the trailing edge of the remaining flute away so it would not interfere as it is on a slight angle.
I put it in the mill and ran it at a low speed and feed to cut the serrations. Depth of 32TPI is a bit over 0.020" so I only cut 0.020" deep. With the hard slide, I took 0.005" per pass and made several passes at full depth to clean things up.
flat the serrations with a flat file to remove the sharp edges.
You don't need the 32TPI tap, it was convenient to me so that is that what I used. A 3/8"-16 can do the same thing, make one set of serrations and then lower the cutter 1/32" and cut a second set. A 1/4"-20 can be used for 40 LPI etc.
You can cut two rows of serrations at 90 degrees or some other angle to checker or flat knurl a surface. I have used this on other items such as a magazine release. It is a simple method of detailing a part.
I have quite a few pics of the build, if there is anything you want to see, let me know, if I have it, I will be happy to show it.