20-28AWG: small signal wires.
The die is the key, they have specific size and shape. 20AWG = 0.81mm, 28AWG=0.32mm in diameter.
you need the right crimper to do a good job.
Show us pictures of the connectors you want to work with, I can make recommendations.
...and here are photos of the ends - they do look about 3.9mm or 4mm in diameter. What crimpers do you use at the Woosh factory?