Trying to identify silver mica cap. value...

[ammel68]

I'm trying to determine the value of some silver mica caps that are soldered into a PCB without having to unsolder or cut their leads to measure them.

The caps are a dark purplish-brown in color and have 20J, 300V, and CDM on them.
The voltage rating is self explanatory and I think CDM may mean they're manufactured by Cornell Dubilier, but does the 20J mean they're 20pF?

Thanks...

 

[kevinkr]

Should be 20pF 5% tolerance..