There is no substitute for a ratcheting crimper. MCM sells a nice one that is color coded to the terminal. Terminals are colored for the wire size range they are meant for. The intent with crimping is to form a "cold weld" as Don hinted above, a proper crimp forms a solid mass of metal with no air gaps between strands. However, we still don't trust that and use uninsulated terminals and solder every one after a solid crimp and tug test. We reserve insulated crimps for the practice robot and prototypes simple to save time in assembly. When the wire size is too small for the terminal you have (fan wires for instance) simply strip long and fold the wire once or twice to fill the terminal before crimping. If you use the Thomas and Betts style crimper (
http://www.specialized.net/Specializ...2X190_PLI.jpg), the tool has an opening with a "tooth" on one side. The terminal should positioned so that the tooth is opposite the side with the seam on the terminal. When crimped the seam should not open. If it does, remake the connection.