I'm going to be quite honest here and say that I don'r use a whip finish tool. I used to but found a quicker method. Once you've got to the head of your fly and the thread is ready to e tied off simply hold the thread tight and spread superglue on the inch closest to the fly. Then wrap it round about three times. The thread will instantly bind down tight. If you want to varnish over this feel free. I personally don't bother. This is a pretty simple and effective way to secure your flies. It also has the added advantage of drying quicker.