I recall there being a discussion on identifying knock filters and what they basic application would have been by the numbers printed on them. I can't seem to find this thread again. I can only find some discussion on identifying through resistance between two of the legs.

I'm trying to set up a MEMCAL for a friend who is converting a friend of his firetruck to TPI. It would be nice to get the knock filter as close to proper as possible, and would like to do it by swapping a knock filter onto a MEMCAL, or finding a MEMCAL that I already have that has a good match.