Thanks! There isn't enough room for the threaded base and nuts on the Pro 4000, so it has to be like this. You don't get the same fine adjustment, but frankly, it is not needed. Especially since the Pro 4000 can't take as long cases as the Six Pack Pro. I did try this style on the Six Pack early on, but was worried you would end up with not finding the right adjustment for some obscure cartridge I hadn't thought of. It's quicker to adjust up and down, but also introduces a tiny bit of movement between the base and the body.