Originally Posted by Doug Fattic

I would check the threading on the seat binder bolt. The Brits used a Whitworth 9/16" during the classic period. I don't know when they switched to metric binders. Sometimes they can be M8 in other countries or M6. When I was learning to build frames in England in 1975, almost all binder bolts were not metric but rather Whitworth threading. See if it is metric or Whitworth. Besides the threads it is possible to tell by the size of the hex key too. That binder on this frame looks like it was made by Andrew Hague in the UK.