This tool crimps by having a U indent on one jaw blade and a smaller u sticking out on the other jaw blade. They did not line up on the one I got, off by about 1/4 so the u that sticks out was at 1/4 of the U that is the dent instead of at 1/2. The other interesting about this tool is that the tool is very wide, more than twice as wide as the other crimping tool I have (IDEAL 9-1/4" Multi-Crimp Tool from Lowes). That seemed like a nice thing at first but it greatly lowers the force per square inch you can place on the crimp as the crimp is more than twice as long. In comparing the crimps, the Ideal crimp tool produced much stronger crimps. The finish on the tool was nice and it was very smooth to use. Perhaps mine was just a dud but with the issue of the extra wide jaw, I had no need to risk trying another one.