Micro-flites were one of several inventions of Frank Eicholtz of San Diego, CA. He was the first to use fiberglass developed during WW II. The company that developed fiberglass was Narmco and the product was called Conolon. It was used in the first fiberglass fishing poles. Frank put it on his bows, and did the same for Howard Hill and Harry Drake. Harry used it to set flight records.
Frank had a business partner in the 1950's and they made the Micro-flite shafts, unfortunately the partner died in a car accident and Frank lost business as a result.
My #10's are spined at 72#, but shoot better out of a lighter center-shot bow. The older spine charts were based on 1950 bows, and noncenter-shot bows that handled lighter spined arrows.
Bob Swinehart used Micro-flite arrows, #10's with another shaft inside for his 100# bow in Africa.
For more information on Frank Eicholtz, and his inventions, read "The Traditional Way" by Fred Anderson.