This is a quick test for the threaded base of a standard North American light bulb. I'm planning to rewire a fixture for 12 volts DC and LEDs. This base isn't totally necessary, but it is a fairly reasonable way to attach the LEDs to the existing bulb location. I think my eyeballs and calipers worked fairly well as it screwed right in on the first try.

Probably not a good idea to use this on a high voltage AC circuit.