Airport Extreme Base Snow power supply

[PaulexPC]

I have an old airport extreme base station, the one that looks like a white gumdrop. (photo below). It's missing the power supply. I have one with the correct voltage and amperage, but the pin is the wrong size. (5 volts, 2.4amps, center +)

Does anyone know what the power supply pin size is?

 

[PaulexPC]

I think I have figured it out.
It is 4.75mm outer diameter, 1.7mm inner diameter.
With a Radio Shack Adaptaplug system it's a size C.

(just in case other people are interested)