Reddit reviews Delphi 12015870 Metri-Pack Female Loose Terminal 630 Series 16-14 Ga-25Pack

Yup, the kit included the wrong tool. Those dies are for the right style of terminal (open-barrel), but completely the wrong size -- they're enormous! You could happily crimp 9.5mm terminals onto 4mm2 wire with the big nest there! The smallest one doesn't look like it's anywhere near small enough for 0.64mm terminals you're using.

If you're not opposed to spending a little more, this is the best hand-crimper ever made for open-barrel terminals. It's non-ratcheting, so you don't have to hassle with adjusting the shut height for different wire gauges, just go until your calibrated wrist says the copper stopped moving. It has an enormous range of nest sizes, able to crimp everything from the minuscule "mini-50" terminals found in certain automotive applications, to the gargantuan 9.5mm beasts in power applications and everything in between. It'll do your Dupont wires (and every other 0.64 terminal) up real nice.

(The one thing it doesn't do is short-crimp terminals like JST's. For those you need a narrow jaw like the Engineer PA-series tools.)

Also, check out the best page on the internet about open-barrel crimp tools, terminals, and quality. I couldn't have written it better myself.