There are many types of automotive and marine electrical connectors. Some of the common electrical connectors are butt connectors, ring terminals, spade terminals, and quick disconnect connectors.
Butt connectors are used to splice two wires together.
Ring terminals are used to connect the wire to a stud point like a screw for grounding or similar.
Spade terminals can be used like ring terminals but the nice thing about the spade terminal or fork terminals is that the stud does open to connect to it. The spade can slide around the stud for a connection.
Quick disconnect connectors are used to connect to a tab and come in four tab sizes,.110 tab is 1/8 inch,.187 tab is 3/16 inch,.250 tab is 1/4 inch and.375 tab is 3/8 inch. There are male and female quick disconnect connectors the female will slide onto the male tab. Other electrical connectors include copper lug ring terminals, crimp caps, t tap connectors, plier tap connectors, hook terminals, and pin terminals.
Electrical connectors can be insulated or non insulated and come in various types of insulation. The non insulated electrical connector is usually bare copper that has a tin plating. Insulated terminals can come in PVC insulated, nylon insulated and heat shrink insulated. The PVC insulated type are usually the cheapest and most common. PVC tends to be a harder insulation and can crack when crimped and for this reason I do not recommend using them. Nylon insulation is a softer insulation and will not crack when the terminal is crimped. The nylon insulation will also withstand higher temperatures. I recommend using nylon insulated terminals and connectors. Heat shrink insulated terminals and connectors are great for applications where the terminal is exposed to outside elements such as high temperatures, rain, snow, and underwater applications.
The heat shrink insulated terminals with adhesive lining create waterproof connections to the wire. Although heat shrink terminals can be costly they are the best connectors to use since the will last the longest and almost never corrode.
When purchasing electrical connectors it is best to use UL listed terminals and connectors to make sure you are getting quality connections. I recommend staying away from terminals and connectors that are made in China due to the low quality standards and cheap materials they use to make the connectors. If you search the internet you can find quality terminals and connectors at reasonable prices.