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In electrical terminology, a toggle switch can have one or more "poles" and "throws." Apole refers to the number of circuits controlled by the switchusually, this is the number of outwardly-visible "levers" on the switch. A throw refers to the number of positions a switch has. Usually, for simple on-off capability, you'll want an SPST switch. To ensure you select the right toggle switch, check with the manufacturer or ask a salesperson to help you. Ensure that the switch is compatible with the device you intend to use it for. Read through the instructions or paperwork that come with the switch to make sure it will work for your purposes. However, if the device you're attaching your toggle switch needs more than basic on-off control, you may need a more complicated switch. For instance, if you're installing a toggle switch to control a car's hydraulic system, you'll probably want a switch with multiple poles to control the hydraulics for the different sides of your car and/or multiple throws so that you'll be able to set the hydraulics to "off" or varying degrees of "on", rather than just simply "off" or "on." Note that there are differences between British and American terminology when it comes to the colloquial names for common switches. In the States, an SPST switch is also called a "two-way" switch, whereas in Britain, it's called a "one-way" switch. Similarly, in the U.S. and Britain, an SPDT (single pole, double throw) switch is called a "three-way" and "two-way" switch, respectively. Different electrical devices require different amounts of current to power them. When searching for switches, make sure the contact rating of the switch you select is equal to (or greater than) the circuit current you plan for it to regulate. Your toggle switch is useless if it can't connect to the device it's supposed to operate. Be sure to pick a switch that's compatible with the electrical connections inside your device. If you don't, you may find yourself having to make improvised connections with a soldering iron, electrical tape, etc., which can be daunting for the inexperienced. Common types of switch connections include: Screw connectors. Solder lugs, pins or terminals. Wire leads. If your device comes with spaces specifically designed to accommodate toggle switches, you may be able to get away without having to make any extraneous modifications to your device. However, the types of devices in which toggle switches are often installed usually don't. Thus, you should usually expect to need to drill a hole for the switch and to install a mount to seat the switch in. Often, you'll need a type of mount called a panel mount that interfaces with a type of switch called a panel switch. A panel mount switch has a threaded body that protrudes up through a hole in a panel and is secured to the panel with a panel or jam nut.
Select a switch with the appropriate number of "poles" and "throws" for your purpose. Choose a switch rated above the maximum current (in amps) that will flow through the switch. Select a switch with the right type of electrical connections for your project. Pick a suitable mount.