In one of Ken's posts he said he designed the Estes converter, which marketing released initially in a starter set, but the rocket in the set was named "Screw Machine" which Ken objected too, and was eventually dropped and the Converter kit was introduced using the same plastic screw couplers. I found that funny. It took years of searching, but based on his story I eventually found and got a "Screw Machine" rocket. RIP Ken.