There are special crimping pliers made especially for mechanically fastening connectors of all types (butt, fork, ring, faston). They usually work for a range of wire sizes (10-24). The upper jaw has a protruding punch and the lower jaw has a matching die. Once you insert the connector into the pliers, and the wire into the connector, you apply force to the handles and the result is the pliers actually pierce the connector into the wire. This makes for a pretty sound connection. Usually the wire will break before the connection fails.
I myself prefer soldering and heat shrinking connections.
http://www-public.tnb.com/contractor/docs/stakon.pdf
