[TCML] sucker gap material

[Dan Casaregola]

I'm building a sucker gap, and was wondering whether stainless steel would be acceptable as gap material as opposed to copper or some other metal.  I have a neighbor who tells me not to buy any type of fittings since he has plenty (all stainless steel).  Second question; what size opening is appropriate in the gap?  Larger opening allows greater flow of air, therefore better cooling?  Or smaller opening causing increased pressure of air stream?  Thanks  Dan