For wiring projects "on the fly", many people strip back two wires and twist them together. This usually makes a decent electrical connection (if twisted tight). But you run into the same trouble as with bare wires - bare metal may short out an electrical connection or break it if come untwisted. Fortunately, some clever people over the years have invented connectors to place on the ends of wire and cable to make good electrical connections that are mechanically easy to work with.
Here are some recommended connectors to consider based on typical projects:
Breadboards and many perforated boards come with 0.1 inch hole spacing. There are deviations from this including Xbee radios as an example. A number of connectors support 0.1 inch spacing. Adafruit premium ("rainbow") jumper wires have female or male connectors with individual 0.1 inch headers on each wire.
There are quite a few types of power connectors. Some common ones you will find:
- 2.1 mm power connector is very often used to connect low voltage power supplies to circuit boards like an Arduino Uno. When wiring these up, be sure to match the positive and negative wires to the right connections on each side. A common configuration is positive on the inside conductor but there are exceptions out there. If you need to make a 2.1mm connector, there are adapters with screw terminals to make it easy.
- JST-PH is the connector used on common 3.7 volt lithium-ion batteries and 3 to 6 volt battery packs.
- USB conections and cables are now commonly carrying 5 volts for portable electronics. The main power connector on the Raspberry Pi is a Micro-USB connector.
Radio Frequency Use
Circuits that have higher frequency signals should use specialized cables and connectors. Often coaxial cable is used to provide a known electrical characteristic and shielding profile. This helps keep signals from bleeding out to unwanted places and matches the electrical characteristics of the cable and the connection. Common RF connectors are SMA (and RP-SMA), uFL, and BNC. Adafruit carries a number of these connectors and accessories. Digi-Key and other large parts retailers will have good selections of RF connectors. You may wish to refer to more in-depth information on RF connectors and RF wiring for specialized uses.
Besides Cable Glands for box connections, there are waterproof in-line connectors that are very handy for keeping water out of connections which need to be disconnected now and then. Shrink wrap is also goof for weatherproofing or special wrap for food environments.
Audio and Video
In between low signal and radio frequency, A/V signals often have special connections. The standard is called the RCA connection, used for audio and older NTSC and PAL standard definition video. High definition video most often uses HDMI cables. Many non-fidelity audio signals are wires with different connections ranging from terminal blocks to banana plugs.
Network and Telecom
Telephone wire in the U.S. uses an RJ-11 jack while Ethernet LAN copper connections use an RJ-45 connnection. The connectors are most often placed onto 8 conductor LAN cable with a specialized crimp tool.
Other Multiconductor Cables
Many other cables have metallic pins which crimp on each wire and then the pins are held together in a connector assembly. A general purpose crimp tool can make such pin connections easier. The specific connector should be selected according to your application.