Open barrel connectors look like this:
The tabs that are sticking up are rolled over by the crimper. The smaller tabs crimp the wire, the larger ones crimp the insulation to provide support for the wire. Insulation support is critical to long-term reliability of the connection. Without the insulation support, vibration will tend make the wire fatigue and crack right were it enters the connector.
The crimp connectors you get at your local Radio Shack or auto parts store are the "closed barrel" type. If you look at the end of one you'll see the metal rolls all the way over in a round or barrel shape. They are meant for the typical crimper you'll also buy at Radio Shack or an auto parts store. Those crimpers CANNOT be used with open-barrel connectors.
AMP sells open-barrel connectors under their FASTON brand name. FASTONs don't normally come as individual connectors, but in continuous strips meant for automated machines. You can cut them apart with a pair of side cutters to get individual connectors.
They come in a huge variety of sizes, materials and configurations. The ones I've used are:
AMP part #41771 - .250" female spade, brass, for 18-22 gauge wire
AMP part #41202 - .250" female spade, brass, for 14-18 gauge wire
AMP part #41449 - .250" female spade, brass, for 10-14 gauge wire
I bought spools of 100 FASTONs from Digi-Key http://www.digikey.com. In 100-count spools, they are about a dime each.
Tyco carries them: http://catalog.tycoelectronics.com/cata ... u/en/17703 . British Wiring sells individual open-barrel connectors http://www.britishwiring.com . A Google search will probably find many other suppliers.
They look like this in a strip.

I have a Paladin 1300 crimper (http://www.paladin-tools.com). It uses replaceable dies, so you can use it for all sorts of crimping duties. Bare frame retails for around $40, with dies about $25. I got mine used on eBay for like $15. Paladin die #2033 makes F-type crimps.
This is what a FASTON looks like crimped with my Paladin 1300. In addition to being a superior electrical and mechanical connection it also looks completely factory. Excellent for restoring old wiring to like new - cosmetically and electrically.

Todd