Primary Coil parameters?? wire size and spacing...

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Original poster: "Bill Vanyo by way of Terry Fritz <twftesla-at-qwest-dot-net>" <vanyo-at-echoes-dot-net>

I'm reposting a previous question (no response first time around):  
 
For my first coils primary, I used 1/4" copper tubing and 1/4" spacing
between the turns (1/2" between turn centers).  That was with three
15/60 NST's.  For my next (second) coil, I'm adding a fourth 15/60, and
would like to someday replace the NST's with a pole pig.  For this next
coil then, should I use 3/8" tubing and/or 3/8" spacing between turns?
 
        Thanks,
        - Bill Vanyo