These LEDs are for installing into switches which support the addition of backlight LEDs.
They are compatible with Cherry MX, clear-top Gateron, as well as Kailh Speed switches.
*Note: Long leg of LED is positive, short leg is negative. By convention, the square pad on a PCB is positive, so the long leg should be inserted into the square pad. Some PCBs may be different, so test with one LED first to make sure it works before installing all of them.