I have the Klein jig. Have never tried the Baxter one. I believe Soren Berger has a set up for sale also. I have found the 16 tpi to work fine in just about any wood. I did try the CA glue to chase the threads in the softer woods (BLM, Madrone, English Walnut, and others) but either I never figured out the proper way to do it, or it just won't work well enough for me. Seems like there was always glue spill where I didn't want it and couldn't clean it up properly. What I do now is cut the threads to about half depth. Then I chase the threads with some oil/wax bowl mix or just some oil (Mahoney's or The Doctor's Woodshop). This lubricates the wood like wetting wood to help you remove tear out with one or two last cuts. I then take 2 or 3 more cuts, lubricating between each cut, till the thread is to full depth.
I would not want threads coarser than 16 tpi. Reason is that with this thread count, you only have to remove at most, 1/16 of an inch to line up the grain, which I heard some one call 'timing' the threads. If you use 8 tpi, then you can have to remove 1/8 inch of wood on the shoulder to line things up, and that might mean you have to cut the threads farther down, which means having to remount and re align the threads with the cutter again, which means way too much work.
I did discover a way to time the threads every time, so you don't end up with one box that needs just under 1/16 inch of shoulder trim (almost 1 full rotation of the part on the jig), and the next one needs maybe 0.005 inch removed (maybe 1/16 of a rotation). It involves 2 things. First, the male thread (on bottom part of box with the Klein jig) has to be cut onto a tongue that is exactly 1/4 inch tall. The other part is a spacer block, and I use a 1/2 inch piece of plywood. The box parts are mounted on pine waste blocks that have nuts epoxied into the bottoms of them. I make a pencil line on the box parts where the grains line up. When cutting either piece, which is screwed onto the threading jig, I rotate the piece till the pencil line is at 12 o'clock, then slide it up to the cutter with the spacer block to tell you how far to slide it, then lock it in place. I use the same timing/lining up method for the bottom of the box. I found, with mine, that I have to back the bottom one off to about 11 o'clock, which leaves me with just a hair of 'adjustment' to the shoulder. Note, you have to screw the bottom piece out farther away from the jig, than you do with the lid (about 1 inch compared to 1/2 inch). This is because when you are cutting the lid, you only have to back it out far enough for the cutter to clear. When you are cutting the bottom threads, you have to totally remove it from the threading jig to test the fit. So, try one first with both the pencil line at 12 o'clock, and then see how much you have to adjust the timing of the second piece. The spacer block allows the cuts to start at the exact same place/rotation spot every time, and the exact 1/4 inch lip on the bottom part means it will screw down the exact same depth every time.
robo hippy