Bob, I do believe you are confusing Durax with Duprat when you describe the
hexagonal section.The Duprat was I believe a brazed up construction like the
round Chater Lea type you mentioned. Durax's "Service Course" were the top
job from them and they were of conventional forged construction.. Cyclo made
fine cranks and double rings, some rivetted together. My favourites are 3
arm FB and Magistroni. One of these in crisp original chrome with Simplex
adapters and rings is the ultimate steel 50's transmission.
Mark, Dingwall. Scotland