I bought one of those fairly inexpensive crimper tool kits from amazon. It came with a great deal of molex type connectors and the metal connectors to thread inside.
I found it fairly difficult to make clean, well crimped connectors, despite the instructions. It took a fair amount of practice to get it "right".
Took a certain pressure, or the plug wouldn't work, too much and the crimper would pretty much crush the plug.
Probably went through 20 or more connectors, before getting 2 that worked. After that I put the tool down, hope to not have to use again!