Here you can see the "double" part of the double crimp. Both the barrel and the strain relief have been crimped thus the term "double crimper".


One area to be aware of is the spacing between the wire crimp die and the strain relief die and the terminals you are using. Here the spacing is a bit wide.


Once you choose a double crimp tool experiment with different brands of three piece terminals to find the best match. Once you have a good match stick with that terminal and that tool.