Lau, Gary wrote:
I'm similarly skeptical about a propeller gap's quenching.  The only 
thing that I can see superior quenching-wise is that the air flow 
over the gap may be better than in a cylinder gap.  But if that was 
all you need for superior quenching, then an air-blast gap should be 
the best solution of all.
Say, the one's designed by Marx? (of high voltage fame, not economics)
see http://home.earthlink.net/~jimlux/hv/blastgap.htm
I think one could do quite well using copper pipe caps (sweat on) with 
a hole drilled in the center.
I believe someone on the list has made a triggered version of this