Fred Krafft gave a paper at Indianapolis in 1979. It was titled "Single-Twist Bunching" and the abstract is as follows:
"Evaluation of desired strand quality, production cost, and savings of insulation is required for choice between single-twist and double-twist bunching for production of flexible conductors smaller than about #4 AWG. Single-twist and double-twist bunching, product quality, construction differences, and economic factors are considered. One advantage of single-twist bunching is the savings in insulation due to the smaller diameter smooth strand."