spark gap

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: mark@xxxxxxxxxxxxxxxx 

Can someone point me in the right direction for working out the gap 
for my spark
gap ???

I'm using a 15Kv 20ma NST with a cap of about 0.0042uF, I'm planning on using a
piece of off cut 3" acyrlic pipe with 3/4" copper pipes bolted around the
inside, however am at a loss on how to check this is feasible and what sort of
gap I should leave between each pipe.

Cheers

Mark