> 
> This sounds an awful lot like homework.
> 
> If there is a finite list of spacings, you can figure out the
> ideal diameter for each one (by reversing the formula), round each up to
> the closest permited diamiter, and choose the one cooresponding to
> the smallest computed value (using the given formula).  Look at
> Array#collect, Array#find, Array#sort, and Array#first.
> 
> -- MarkusQ

I assure you, this is no homework. I am complete newbie, and I am 
creating a plug-in to work with SketchUp. I could email it you if you 
would like to see.
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